The game where you can play as a caveman character. It's sort of set up like a Mario game. You fight dinosaurs in it. I used to play that all the time as a kid.
Bonk was on the Turbo Grafx 16. I almost bought that system, when I already had a Sega Genesis. I came really close when I heard they had a cd drive for it already and this one reviewer said he loved fighting aliens and he could load up his Metallica music while doing it. I almost did it for that and Slaughter House.
I think the OP was talking about this game. I saw it once and thought is was a weird concept.