Onomatopoeia of a headboard repeatedly striking a wall, ostensibly due to people fucking in the bed that holds said headboard.
I couldn't sleep last night because Jared and his girlfriend in the apartment next to mine were fucking for most of the night. All I heard was "ka-thunk, ka-thunk, ka-thunk", punctuated by an occasional moan or loud request for one party to fuck the other one harder. I let the air out of that faggot's tires for that.
think (or any form of the word "think")
i did not ka-thunk up the word ka-thunk; it was invented by someone i kno. but i ka-thunk that the word ka-thunk deserved 2 b n a dictionary of some sort.