What does "to be Latin" mean?
Solution 1:
OED has this for Latin under "Draft Additions 1997":
Designating the characteristics of temperament or behaviour popularly attributed to European or American peoples speaking languages developed from Latin: proud, passionate, impetuous, showy in appearance, etc. Sometimes somewhat dismissive.
Its first citation for that meaning is from 1914.
Solution 2:
The stereotype of the passionate 'Latin'
An editorial titled "Things That San Francisco Has," in the San Francisco [California] Call (November 17, 1912) describes what its author takes to be the characteristics of the "Latin" spirit:
And another thing is the spirit of San Francisco. This does not mean that spirit of "gay courage" which rose to meet calamity [the great earthquake and fire of 1906] undaunted and started the rebuilding while the ruins still smoked. Nor does it mean the spirit, rather Latin than Anglo-Saxon, which makes this a carnival city, a city of amusement, of pleasure, of impulsive, warm hearted cordiality.
The "Latin" here is probably tied—at least in part—to the Latin American influence on San Francisco, but the author may also have in mind the substantial populations of citizens of Italian and Portuguese ancestry in the city.
The stereotype of people from "Latin" countries as being more enthusiastic, passionate, and volatile than the Germanic people to their north goes back farther than that, however. For example, from an untitled item in the [San Francisco] Daily Alta California (December 16, 1871):
There is an amount of ferocity about the Latin character sometimes appalling. In all of the dreadful occurrences in which human passion has played so conspicuous a part during the year, none is calculated to cause a deeper thrill of horror than the execution of the young students in obedience to the clamors of the infuriated Volunteers in Havana. The young men were suspected (nothing more) of having broken the glasses which were placed on the graves of some volunteers who had fallen in the civil strife which has for a long time been raging on that island [Cuba], and of having substituted garlic for flowers strewn there. If students had been guilty of such a mad prank among us, probably no severer punishment would have been meted out than dismissal from college. Allowance would have been made for the indiscretions of youth.But in Havana the ringleaders were summarily executed, and all the others except two sent to the Penitentiary. In the Communist excesses in Paris nothing like this has ever happened. It is the saddest tragedy that has ever been enacted under the sun.
It is unclear whether "Latin" in this case refers to "Latin American" or to "Southern European," as Cuba was governed and administered by Spain in until 1898.
From "At the Lyceum: Salvini in 'The Three Guardsmen'," in the [Ithaca, New York] Cornell Daily Sun (January 27, 1894):
But a successful "Don Cæsar" or a "D'Artagnan must, it seems, be of a Latin temperament to infuse the fire and zest into these plays, without which they loose their interest. Salvini gives to the intrepid young Gascon of Dumas" all the fire and impetuosity of his Italian nature. He is young, handsome, and vigorous, and while he is in possession of these elements so essential to romance, he will continue representing the popular plays of Hugo, D'Ennery and Dumas.
Alessandro Salvini was a famous Italian actor.
From "The Prospect of Peace: Spain Is Believed to Be Sincerely Anxious to End the War," in the New York Sun (August 2, 1898):
The destruction of Cervera's fleet was, in the opinion of nearly every official here [Washington, D.C.], the underlying reason for the decision at Madrid to make the inquiry presented by M. Cambon, but some of these officials say that, with the mercurial tendency of the Latin character and the intense pride of the Spanish people, there lies the likelihood of a complete change in the sentiment that actuated the Sagasta Ministry In determining to ask this Government if it were willing to make terms for ending the war.
This description of "the Latin character" may reflect the fact that the United States and Spain were at war at the time that this article appeared. From Marquise de Foutenoy, "Holland's Young Queen: Her Coronation Will Be a Red Letter Event for Her Subjects" in the El Paso [Texas] Herald (August 27, 1898), reprinted from the Washington [D.C.] Post:
I have often heard it said that the Dutchman is at heart a republican, and cares but little for the pomps and ceremonies of court life, which do not appeal to his sense or stir his imagination, as is the case with more warm blooded Latin races. Either this theory is untrue, or else the worthy Hollanders have permitted their devotion and affection for their young queen to get the best of their democratic sentiments. For they are certainly sparing neither money nor trouble to celebrate in a fitting manner the coming of age of "Hare Majesteit de Koningin."
Here the "Latin races" almost certainly refers to the peoples of Southern Europe.
From "The Theatrical World," in the [Sacramento, California] Record-Union (July 16, 1899):
One of the most suggestive articles on [Sara] Bernhardt's "Hamlet" is in the London "Times." The writer says that Madame Bernhardt "makes Hamlet a pleasant, humorous, very gay prince, who in happier circumstances would have been the life and soul of the court—a merry trifler with old Polonius, the first to welcome any diversion such as the traveling players afford, a companion of Yorick would still have delighted to consort and jest with. Hamlet, as Mme. Bernhardt reads the part, is less the moody Dane than a full blooded Latin, full of energy, readily provoked to tear passion to tatters, to break out into violent declamation or denunciation, and really feeling that it is a 'cursed spite' which sets him to remedy the out-of-joint time."
The source of this quotation is an English reviewer for the London Times, it seems probable that the characterization of "a full blooded Latin" and presumably reflects the writer's views of European—rather than South American or Central American—"Latins."
A stereotype of the "hot blooded Latin despot" of the Americas appears in an untitled item in the [Nyack, New York] Rockland County Journal (November 27, 1909):
Zelaya, president of the petty Central American republic of Nicaragua, needs to be dealt with promptly and effectively for his summary execution of two young Americans whom he charged with assisting the revolutionists against his own tyranny. The hot blooded Latin despots of that part of the western hemisphere must be taught that to take the life of a United States citizen, or even to ill-treat him, is not a light matter in the estimation of this government.
In this remarkably arrogant and jingoistic news item, the writer is applying the Old World stereotype of the "hot blooded Latin" to a Central American dictator.
From "True Stories of the Secret Service: A Shattered Romance," in the Salt Lake [City, Utah] Tribune (May 29, 1910):
One of the detectives employed in watching the house was a prepossessing young Italian. I will name him Louis Merito. He was well educated and of fine address. Watchful and of a nervous, sanguine temperament, he was nearly always sure of being the lucky one when sent with others to make a capture.
...
It appears that her deep sorrow, her soft, words, and above all, her fears, had quite bewildered him. Real beauty in distress was too much for the warm blooded Latin, and he surrendered unconditionally. In impassioned terms he declared his love and offered her his heart and hand.
It is unclear from the article whether Merito was an immigrant from Italy or an American-born citizen of Italian ancestry.
And from "Over All America?" in the Norfolk [Nebraska] Weekly News Journal (February 24, 1911):
Ir will be a long time before the stars and stripes are extended over any very considerable additional American territory. Some of it needs our control badly enough, goodness knows. But Americans do not like the idea of having their domestic affairs settled by representatives in congress from the hot blooded Latin bred races of the tropics.
This paragraph appeared in connection with an assertion by a U.S. politician "in a semi-humorous vein, that he believed the stars and stripes would one day float over the entire western hemisphere."
The stereotype of the subtle 'Latin'
On the other hand, there is a somewhat crosswise tradition in English writing of the "Latin temperament" as being one of subtlety and indolence in cotrast to northern European bluntness and vigor. For example, "Ultimate America: A Striking Lecture by Rev. Joseph Cook," in the Burlington [Vermont] Weekly Free Press (October 26, 1877):
We are descendants of the old Norse pirates. It was as pirates that ou fathers first appeared, sailing the great German ocean, on robber voyages. We have even yet a tinge of our forgotten ancestry. And the American can eliminate is producing a Latinized temperament and with the Latin temperament always comes finesse. But we have far more vigor than the Italian or tho Greek. Our great tradition as a race is that we love honesty.
And modesty, he might have added.
From an untitled item in the Cambridge [Massachusetts] Press (October 5, 1889):
The immense popularity of the late Wilkie Collins' creation of Count Frisco in "The Woman in White" was due to the fact that it embodied the popular English conception of the Italian and French character. Englishmen of classes, and especially the entravelled ones, invariably connect something sinister, mysterious and underhanded with the Latin temperament. Plays in which such a character appear are always applauded. The fine manners, the engaging frankness, the deferential politeness are all considered so many masks for the concealment of some treacherous design. Even Dickens repeats these types of the Latin foreigner in some of his best novels, and especially in that novelette which he afterwards dramatized in collaboration with Wilkie Collins, "No Thoroughfare."
The stereotype of the insouciant 'Latin'
Yet another stereotype is evident in this excerpt from "Guatemala: And How She Cares for Her Criminal Classes," in the [St. Paul, Minnesota] Appeal (December 11, 1897):
Everybody seems as cheerful and unembarrassed as if to be in "durance vile" were the most natural thing in life—the men in the shops particularly appearing much more happy and carefree than their fellow-workman in shops outside the walls whose daily bread, maybe, is not so assured. Probably this comes (from the happy-go-lucky Latin temperament and the lack of aspiration which makes these people fit easily into any rut where fate may let them fall.
Here the "Latin" people being described are Central American.
Conclusions
The original association of a supposed "Latin" temperament with strong passions almost certainly refers to people from Southern Europe, not Latin America, and this orientation remained strong even in U.S. newspaper descriptions of "Latin" in the early twentieth century, although the competing sense of a "Latin" temperament as one characteristic of the populations of Central and South American was already in evidence by that time in the United States. I imagine that for a British writer of the 1930s (such as Agatha Christie, in Death on the Nile) the association of "Latin" with "Southern European" is even clearer.
The stereotype is undoubtedly much older than the late nineteenth century. Merriam-Webster's Eleventh Collegiate Dictionary (2003) cites instances of Casanova in the sense of "lover" from as early as 1852 and instances of Don Juan in the sense of "seducer" from as early as 1679. And, of course, Romeo, the prototype of the intemperately ardent lover and young gentleman of honor, dates to 1595. Edgar Allan Poe's "The Cask of Amontillado"—which is set in an unnamed Italian city at carnival time and hinges on the elaborate revenge killing by Montresor of Fortunato, who had "ventured upon insult"—was published in 1847.
A contrasting stereotype of the Latin temperament as crafty and subtle, is also of long standing in the English-speaking world, as is yet another stereotype of it as indolent and happy-go-lucky. The contradictions of these various images doesn't seem to have bothered the writers who propagated them. I suppose that as long as they didn't use conflicting descriptions of "the Latin character" in the same piece, they could appeal to whichever prejudice suited their immediate purpose.
Solution 3:
There's the stereotype of Latin to mean hot-blooded Latin:
Folks in colder climes can view those in hotter climes as more emotional, passionate, temperamental. Picture the Desi Arnaz character in I Love Lucy when he got angry and thought Lucy had some explaining to do.
Consider that Denmark is the most southern of the Scandinavian countries. Scandinavians (Danes included) view the Danish as emotional. Get it?
Solution 4:
I believe the word was used as congruent to 'passionate' and was(possibly is) still used to describe gypsies and such folk who are usually seen as making merry, being drunk, causing a general ruckus by being 'in the heat of the moment' and not strictly following all the rules of said society.
I have not come across this particular phrasing (as in kill) but I have come across the term itself being used as a description before and I have gathered the above more contextually than by research.