“Boink” is an onomatopoeia.
Some pervert writes:
“Boink”? Yeah, it’s onomatopoeia for sexual activity!
Dear Pervert: WRONG. Sexual activity does not sound like that… I mean, it does if you do it right, but few are that skilled. Boink is the sound of getting hit on the head with an animated object of some kind (which, incidentally, is also a description of correct sexual activity—that may be where the confusion comes from). Get your mind out of the gutter.
For my non-pervert readers, here are some more of my favorite onomatopoeias.
Try using one to spice up your bland, mind-numbing, everyday conversation. I think you’ll be pleasantly surprised by the result.