When did people start "boinking"?

Solution 1:

The OED dates boink as a verb back to 1984, citing Stephen King's Thinner, where it appears to be used as onomatopoeia, similar to bonk:

He half-expected them to begin bopping and boinking each other.

For this sense, the OED gives the definition "to strike, to knock", which is fairly similar to how bonk is used. As for the sexual meaning, their earliest cite is from two years later, a 1986 posting to the newsgroup net.singles by Andrew Tannenbaum:

When you and your honey boink away, you're doing what the doggies do.

Can boink be antedated? Perhaps. But take a look at the following chart from Google Books Ngrams Viewer:

So at the very least, boink wasn't widespread until after the mid-80s.

Searching Google Books, I was able to find some examples of boink from before 1986, but none with a sexual meaning. I chose to search for boinking first to reduce false positives because Google Books (unlike their Ngram Viewer) is case-insensitive and Boink is a name. I did also search for boink, but it was less useful. Searches for boinked and boinks had fewer false positives than boink did, but neither turned up any pre-1986 citations with a sexual meaning.

Most of what I found was like the following snippet from The Complaint Booth (Jack Kurtz, 1978):

Fairies pass through audience boinking people with their wands. Elves up and down aisles "beeping."

Here it seems similar to bonk. And we can find scattered earlier uses with the same meaning, as in the following 1966 use with a similar meaning in Science & Technology:

This causes a mechanical wave to travel around the circumference of the sleeve―in the same way it would if you kept "boinking" the top of a metal can with your fingers.

Using the same tools, Frank found an even earlier example, apparently quoting something Senator John Thye said in a 1947 congressional committee meeting:

Mr. Sears, how would you propose to perfect the general farm program, disregarding soil conservation which is just one small phase of the enter program, but boink back to parity price, the ever-normal granary, and those programs?

There are more like this, but it didn't seem to be especially common and none of the pre-1986 examples I found had a sexual meaning. Of course, that doesn't mean people didn't use it that way, only that I can't find it in print using online tools. It seems likely that the word was used in speech before it appeared in print, but I can only speculate as to how much earlier.

Given the dates, including the citation Frank found, it seems reasonable to guess that boink goes back about as far as bonk. As for the sexual use, it seems safe to say it became commonplace after the mid-80s.

Solution 2:

According to the following source the usage of 'boink' by David Angell in the American sitcom 'Cheers' may have predated Bruce Willis's line in 1985.

But it seems likely now that Cheers used it first, though not very long before. Les Charles, one of the creators of Cheers, said, in remarks delivered at the memorial service for David Angell (and his wife, who also died in the September 11th incident): "And lest we forget, if he'd never done another thing in his career, David Angell would have earned immortality as the man who added the word boink to the English language."

• It looks like Angell worked as a writer for _Cheers_ mainly in 1983 and 1984, i.e., the first few seasons of the show; he then went on to work as story editor and producer. Presumably any use of 'boink' attributable to Angell's writing would have been during 1983-1984, predating the 1985 use on Moonlighting. I've not yet seen any concrete evidence that 'boink' was ever used on Soap other than what's said in the Jargon File entry.

Source: www.groups.google.com/forum

The following sentence is from Cheers scripts episode 'Sam and Diane Day' in 1983.

• "Well, last I saw, you and Diane were here alone. D’ja give her a goodbye boink?"

• The actress Carla Tortelli, who appeared in all episodes of Cheers in 1982–1993 ( referring to David Angell):

• "He invented the word boink. Which came from Sam and Diane were boinking, and they were looking for a euphemism for that, and David thought of the word boink. It has since entered the lexicon, which actually, I spoke about that at his memorial service, as part of his legacy."

Source: www.chambersandmalone.tumblr.com

Solution 3:

(It's been bugging me for ages this "boink".)

The earliest instance I found boink, used unequivocally as a verb, is in an electrical engineering volume called R & D Review, 1957.

The analogous picture in a simple mechanical model is that of the bottom of anold-fashioned [sic] oil can just as it “boinks”: there are two stable states separated by an energy barrier. If we had not included the spontaneous distortion (for instance, if the lattice were incompressible but still thermally expansive), then on increasing temperature the interaction energy characterized by T1 …

Thanks also to @josh61's post, I was spurred to watch the American sitcom Cheers for myself. I viewed the entire 11 seasons (1982-1993), and I discovered the term boink, meaning sexual intercourse, was uttered twice in season 3. At that time the shows were written by a staff of writers among whom were David Angell, Peter Casey and David Lee who later worked together in the spin-off show Frasier, 1993-2004. According to Wikipedia, the writers in episode 2 were Glen Charles & Les Charles, and episode 22 was written by Sam Simon (co-creator of The Simpsons).

The first utterance of boink occurs in episode 2, Rebound: Part 2

In Rebound: Part 2 the umpteenth waitress hired to replace Diane Chambers quits her job when she discovers the sex-obsessed but charismatic bar owner, Sam Malone, has bedded her sister. Carla Tortelli (played by Rhea Perlman), Sam's most loyal employee, exasperated by the number of waitresses who quit, tells him:

(0.15.15) Carla: Great, great. Now I've gotta work another Saturday night by myself. Sam you promised you weren't going to boink any more waitresses in this joint unless it was me!

Boink appeared again in episode 22 "Cheerio Cheers" but this time as a noun. The following line is delivered at h0.20.02.

Carla: Well, last I saw, you and Diane were here alone. D’ja give her a goodbye boink?

Episode 2 was aired October 4, 1984 whilst episode 22 was filmed in late November 1984, and aired April 11, 1985. Meanwhile Stephen King's novel, Thinner, mentioned in @snailboat's answer was published in November 19, 1984.

_{^{LINK TO CHEERS SCRIPTS.}}

Solution 4:

I was in a group of teenagers in a small school in Sleaford, Lincolnshire, England who started using the word "bonk" to mean have sex in about 1970. We have always maintained that we "invented" it having never knowingly heard it used before. We set out on a mission to "spread the word". Maybe we were delusional or could it be that we succeeded?