Origin of “ish kabibble” as an interjection i.e. 'What, me worry?'
A lot of words that have a /ʃ/ at the start or phrases that use 'ish' (/ɪʃ/) (like Joe Schmoe or ish kabibble) come from people mocking Yiddish. Yiddish (for a while and I think still currently) was popular in New York where a lot of these expressions came from. It's also where we get 'oy vey'. Upon seeing it, I immediately thought of faux Yiddish, and your research and my own seems to indicate that the term 'ish kabibble' in English is derived from the Yiddish 'nish gefidlt' which means 'It doesn't matter to me'. There seems to be a bit of mystery around it's true etymology, but I'm gathering that faux Yiddish is the best guess we have.
Leo Rosten, Hooray for Yiddish! (1982) offers this account of ish kabibble:
ish kabibble Derivation: unknown; possibly a corruption of the Yiddish nit gefidlt (or nisht gefidlt). 1. I should care. 2. I don't care. 3. Why worry about it?
This extraordinary slang phrase, uttered with a shrug, was often heard from 1917 to 1947 to mean "So what?" or "It doesn't bother me," or (in current cant) "I couldn't care less."
Fanny Brice, the Ziegfeld Follies comedienne and radio star ("Baby Snooks"), seems to have introduced "ish kabibble!" meaning "Why worry?" The phrase caught the attention of the "dean of cartoonists," Harry Hershfield, who launched a syndicated comic strip, Abie the Agent, about the adventures of one Abe Kabibble. It was called "the first adult comic strip" in the American press, and was immensely popular from 1914 to 1932 (Editor and Publisher, October 17, 1970).
A jazz song, "Ish Kabibble ... (I don't care)," became the staple of a trumpet player in Kay Kyser's band (21,000,000 radio listeners weekly), who adopted the name, a shlemiel's manner, a funny haircut, nonsensical logic, and performed as a comic. He was a great favorite when touring U.S. army camps, and for a decade on NBC. He brought "Ish Kabibble" to millions of American children.
The first "Abie the Agent" cartoon that an Elephind newspaper database search finds appears in the El Paso [Texas] Herald (February 7–8, 1914), with the headline "You Should Bibble! Follow His Adventures and Get a Steady Smile." Abie appears to be a car salesman, and he says things like "I want you should see for yourself what a fine smooth car this 'Complex' car is—never balks, never stops. As an agent of the 'Complex' Company I guarantee it!" and "Aha! Right away I got to get blocked by a dumb animal what don't know nothing. Now I got to wait till they hitch him up. Horses should not stay in the way of progress and a sale!" and "Noo noo! Can you beat it! Such a luck. A city full of streets and the one I pick for a 'sample ride' got to have a sprinkling wagon in front of me!" and "Ah klog! Now comes a manhole. It looks today like a plot arranged by Benny, the agent for the 1914 'Collapsible.'" Most readers in 1914, I imagine, would gather that Abie Kabibble was an immigrant from Eastern Europe, living and working in New York City or some other U.S. metropolis, and probably Jewish. In the next day's cartoon, published in the Omaha [Nebraska] Daily Bee, Abie uses such exclamations as "oy" and "geevald!"
Early references to the expression: September–October 1913
The earliest published instances of "ish kabibble" that I've been able to find are from the last four months of 1913. And the first of these is a cartoon with the title "Ishkabibble" by "V. C." seemingly about a Swedish boxer named Axel and his trainer, in the New York Evening World (September 15, 1913). Interestingly, this is five days before Sam Lewis and George Meyer copyrighted their soon-to-be hit song "Isch Ga-bibble" (September 20). Press notices of the song began to appear by late October 1913.
From "Notes of the Trade," in the [New York City] Player: The Official Organ of the White Rats Actors' Union of America (October 24, 1913):
The George W. Meyer Music Co. are having a great run on their three new numbers by Sam M. Lewis and George W. Meyer, "Magical Eyes," "You Must Love Someone," and "Isch Ga-Bibble." Howard & Kyle are featuring the first two numbers, and Gertrude Valerie is doing the same thing with "Isch Ga-Bibble." The firm have just issued a new march and two-step by Joel P. Corin, "San-Fran-Pan-American." "If He Looks Good to Mother, Don't Look for Another" and "Curly Head" are also Finding a large public following.
Copyright entries for this song—spelled alternatively as "Isch Ka Bibble (I should worry)" and "Isch Ga-bibble (I should worry)"—were recorded on September 20, 1913, in the Library of Congress's Catalogue of Copyright Entries (1913).
From "East Liverpool [Ohio] and Vicinity," in The Pottery, Glass & Brass Salesman (New York City: October 30, 1913):
Representatives of the manufacturing potters met Saturday evening with the Independent Claymakers' Union, in response to a request from the latter organization. The manufacturers, it is understood, have announced that they will only deal through the National Brotherhood of Operative Potters, with which organization the claymakers are not affiliated. A strike is probable this week, but as one manufacturing potter put it, "Ishgabibble."
From "Descriptive Review," in the [New York City] Player: The Official Organ of the White Rats Actors' Union of America (October 31, 1913):
"Isch Ga-bibble," words by Sam M. Lewis, music by Geo. W. Meyer; published by Geo. W. Meyer Music Co., No. 145 W. Forty-fifth St., New York City. It will not be necessary to inform many persons that the English for "Isch ga-bibble" is "I should worry." The translating of this nonchalant bit of slang into idiomatic Hebrew was bound to come. No doubt the many other races in this country will transform it into the speech of their fatherland, if they have not already done so, thereby helping to cultivate that sense of personal liberty which is one of the blessings of a free and glorious republic. "I should worry" has taken its place among our most highly prized copybook rules, along with "Honesty is the best policy," "Virtue is its own reward," and "Thanks for the lobster." Both in public and private life we see it applied a dozen times a day. If anything goes wrong politically, in place of joining with our fellow voters to remedy the evil, we shrug our shoulders and murmur," I should worry." If Mrs. Murphy's young hopeful misses his lessons at school and the teacher puts him back a grade, the rising young American hitches up his trowsers, grins at his admiring pals, and ejaculates, "I should worry!" Father says it when he's told that a dozen repeaters have been arrested in his district. Sister Gladys makes use of it when she is told that she is nearly an hour late starting for the office and is in danger of losing her place. It's a fine, independent spirit, no doubt, but there are times when we carry it a little too far, and if we keep on—What's that? Beg pardon, I'm sure! And thank you for reminding me that "Isch Ga-bibble" is a comic song and should be treated as such—not made the subject of a lot of second-hand moralizing. Right, dear boy, but what with all of the political spell-binders surcharging the air with their beautiful and heartfelt encomiums of their brother candidates on the opposition tickets, and the memory of Mrs. Pankhurst's too brief stay among us, it is difficult not to attempt to uplift one's fellow man.
As to the song, it's a right up-to-date comic, all right. In the first four lines a man's best friend runs away with his wife, and "Isch ga-bibble" he exclaims. "I should worry if they steal my wife, and let a little pimple grow on my young life." With such a disposition it is comparatively easy to look on the funny side of things, and author Lewis has dipped his pen in his bottle of comic ink and jotted down a laugh under every second note.
Early references to the expression: November–December 1913
From Sol Kraus, "Paragraphs of Theatricals Gathered in the Rialto of the Golden Gate," in the [New York City] Player: The Official Organ of the White Rats Actors' Union of America (November 7, 1913):
F. K. Snowdon, Coast representative for Shapiro, Bernstein & Co., and Harold Rossiter, is keeping busy supplying performers with "Girl in the heart of Maryland" and "In the Valley of Broken Hearts." He says when you get songs like these you don't have to plug them—they plug themselves. In other words, "Isch Ga Bibble."
From an untitled item in the Mt. Sterling [Kentucky] Advocate (November 26, 1913):
Will Dr. Buschemeyer make good as Mayor of Louisville? Well, ish ga bibble!
From an untitled item in Motor Age magazine (Chicago, Illinois: November 27, 1913):
If the railroads raise the freight rates in Kansas, C. E. Massie, of Westmoreland, will holler indifferently, "Ish kabibble.'' He has made a gasoline locomotive out of a second-hand Mitchell car of a vintage of 1910 and with a mileage record of 40,000 miles. Substituting flanged wheels of standard track tread for the rear or traction wheels and fitting a miniature car truck in place of the original front wheels, he travels between Blaine and Westmoreland daily with his freight.
From "State News" in the [Minot, North Dakota] Ward County Independent (December 4, 1913):
"Ishkabibble" is the word the Jews use when they wish to say, "You should worry."
From "Cheesemakers' Convention Song," in the [St. Paul, Minnesota] Dairy Record (December 17, 1913):
When the cheesemakers meet, / Come early, get a seat, / Down in the middle. / Greet old friends here and there, / Meet new friends everywhere, / Forget your work and care. / Sing "Isch ga bibble."
From "Harvest Time for the Calendar Grafters," from the Snohomish County Tribune, reprinted in the [Olympia] Washington Standard (December 19, 1913):
What cares the itinerant salesman that the hundreds of dollars sent out of town never find their way back? "Ishkabibble" is his thought, which being translated from the mysterious Hebrew into plain English reads, "I should worry."
From "He Yawned When the Alarm Went Off But Didn't Wake Up" in the [Chicago, Illinois] Farm Implement News (December 25, 1913):
But the boom-proof Dealer drew up a Notch, shrugged a couple of Shrugs, expressed one “Ishkabibble,” and failed to Keen.
From "TSIIGARI RULES KXTE I iTAI X." in the South Bend [Indiana] News-Times (December 31, 1913):
The third entertainment given by the Ishgabibble club was in the nature of a dancing party given at the Knights of Pythias hall Tuesday evening. The hall was very prettily decorated for the occasion in holly and evergreens. A very large attendance was present, many being out-of-town guests. Mattes' orchestra furnished the music.
Early references to the expression: January–February 1914
From a note from local number 37, in St. Louis, Missouri, in The Coopers International Journal (Kansas City, Kansas: January 1914):
Now I beg pardon when I say 100 per month, more or less. I am not speaking of silver or gold, but of those little fellows that you need to buy papers with or sneak into the missionary box. Did you get me? Ish kabibble.
From "What Do You Mean by Ish Ka Bibble?" in the Rock Island [Illinois] Argus (January 2, 1914):
"Ish ka bibble" is western slang of Yiddish or, rather, German origin. It started, unless we are mistaken, in Seattle, where it first got into print a year ago. The phrase is a corruption of the German "nicht gefiedelt," which means, literally, "Not fiddled." The Germans, especially of Eastern Prussia, and Jews everywhere have long used in the sense of "I don't care." "Ish ka bibble" is the way American have understood the phrase and spread it.
From Guy Pierce, "'Twelfth Night' Beautifully Presnted," in the Los Angeles [California] Herald (January 8, 1914):
"I guess they are just making an after-Christmas donation to the telegraph companies,” said Manager Harris this morning. “Business is good, so isch ga-bibble.”
From "Rialtografs," in the Los Angeles [California] Herald (January 10, 1914):
Ritchie says: “Ishkabibble. When Murphy whips me for the title my whiskers will be nine feet long and as white as the dome of Mt. McKinley. Bring me another one for February 23."
From "Chicago Notes," in the New York Produce Review and American Creamery (January 28, 1914):
Chicago members of the Elgin Board of Trade who have withdrawn from that board recently were quietly informed of the fact that the Elgin board of trade would refuse to accept their resignations, and, if their dues were not paid by February 1 they would be suspended for non-payment of dues. "Isch Ga Bibble," was the happy rejoinder of the Chicago "bunch."
From "Various Notes," in The Florists' Review (January 29, 1914):
Wm. Salman, the eminent Race street flower seller, recently captured the robber who broke the show window of the jewelry store on Race street. He sits back with an "Ishkabibble" air while others are fighting for the reward.
From an untitled item in the Red Bluff [California] News (February 13, 1914):
When we hear that another $200,080 is about to be given over to the Sacramento River we are constrained to feebly mutter "Ish Kabibble.”
From "'Ish Ga Bibble' Isn't Hebrew Says Toacoma Merchant. What Is It? in the Tacoma [Washington] Times (February 7, 1914):
The Hebrews most emphatically deny that "Ish ga bibble" is in their language, or anything like there language. And they ought to know.
Julius Friedman of Tacoma declares that there is no such word or words in the entire language as "Ish ga bibble." He told me so this morning.
"Then how would you worry in Hebrew, then?" I asked him.
"There is no such word in our language for that expression. The words in German, however, which is almost identical with our language, are Ich sal zorgen."
From "Chat of the Craft," in the [Cincinnati, Ohio] Mixer and Server (February 15, 1914):
“Isch-Ga-Bibble,” or something which sounds mighty close to that, is the way our folks in Seattle give expression to the “I should worry” stunt. Any time you strike the metropolis in the State of Washington you can be sure that something has been built overnight. Gee, but that town of Seattle has grown—and the same thing goes for our locals in that city, too.
Early references to the expression: March 1914
From Harry Davis, "The Principles of Men's Wear Display," in Merchant's Record and Show Window (New York City and Chicago: March 1914):
If you destroy the character of a garment and hide the little "tricks" that have been put in to help sell it, what is there left to attract or interest anyone? Nothing. Well, then, why do it? You don't, you say? Then bully for you. A lot of others do do it, however, so let's get after them, shake 'em up a bit. Of course they will not like it; and they will say we "holler" just because they don't work as we do. But what do we care—ishgabibble! We have been asked to say what we think about the things that go to make “The Principles of Men's Wear Displays” and we shall not say what we do not believe.
From an advertisement for Utah Gas & Coke Company in the [Salt Lake City, Utah] Goodwin's Weekly (March 14, 1914):
"Ishkabibble!"
"Mother has a new gas range; Pa has a gas water heater, the baby has a gas stove and I don't have to carry no more coal
"Hurrah for Gas"
Those are the sentiments of the average small boy. His elders have still more reason to appreciate gas and the liberal terms given by the Utah Gas & Coke Company.
From an unidentified letter from the University of Texas [in Austin, Texas] chapter in The Delta: A Quarterly Magazine of the Sigma Nu Fraternity (approximately March 1914):
We have been giving several whopping good smokers since Christmas for our Freshmen rushees, and are now planning the final scoop on the 24th of this month. The time is rapidly approaching when Freshmen may be bid, May 10, but we believe that we have a goodly number lined up on the right side already.
As I finish this letter, I can hear in the next room heated discussions of Freshmen probabilities, mingled with agitations of the Mexican War problems, but “Isch Gabibble” about the peons, for we are going after the Freshmen.
And finally, here is an item suggesting that Leo Rosten may have been right about the origin of the expression. From "Not 'Isch Ga Bibble, After All, but 'Nisch Gefiddellt,' Investigation Shows," in the Washington [D.C.] Herald (March 26, 1914):
"Isch ga bibble?" "Whaddyemean 'Isch ga bibble?'" asked the Germans who live in Germany when Americans "pulled" the phrase during their wanderings in the fatherland.
"It's German," responded the tourists. "Don't you know your own language?"
...
There is a saying common among German Hebrews meaning about the same thing as "I should worry." The saying is: "Nisch gefiddellt." In a Hebrew theater in New York one of the comedians "put across" the line. An American song writer in the audience heard it, didn't understand the correct pronunciation, and wrote it down the way it sounded to him. 'That's the way it ought to be, anyhow," he remarked. So he wrote an "Isch ga bibble" song and it went all over the country, and everyone shrugged their shoulders and said "Isch ga bibble," and it got back to Germany that way, and now that Dr. [George] Barthelme has found out what it's all about the German mind will be relieved and everybody will be happy, and will say: "Just like Americans, nisch gefiddellt": and the Americans will keep right on saying "Isch ga bibble."
Conclusions
The 1913 Lewis & Meyer song "Isch Ga-bibble" (aka "Isch Ka Bibble") is almost certainly the source from which popularization of the expression "ish kabibble" sprang. It was the "Hakuna Matata" of its time. However, it is not entirely clear whether (as the March 26, 1914, article cited above argues) the expression originated in a mangled transliteration of an existing Yiddish phrase or whether (as the October 31, 1913, article cited much earlier in this answer argues) the expression was a translation into Yiddish of an already popular U.S. English expression—"I should worry."
Yet another twist involves the occurrence of a cartoon titled "Ishkabibble" in a New York newspaper a few days before the Lewis & Meyer song was entered into copyright.
Still, it seems clear that we owe the U.S. English wording "ish kabibble" to the popularity of the Lewis & Meyer tune. Long after "I should worry if they steal my wife, and let a little pimple grow on my young life" vanished from popular consciousness, "ish kabibble" has survived—although at this point it may be more closely associated with a trumpeter with a goofy haircut than with a sarcastically insouciant attitude.