(NSFW) How long has the word "boink" been in use. Where did it originate?

Boink is one of my favorite slang terms for sexual intercourse.
It doesn’t have the taboo power of fuck, it doesn’t seem as vulgar as screw, it has a funny sound and occasionally people sort of smile when they hear it.

Plus, it makes my girlfriend roll her eyes and shake her head in mock disgust.

But it seemed to simply appear in the lexicon rather recently and suddenly.
Where did it come from?