1)Having chaffed asshole. When you have wiped your ass a lot, mostly during diarrhea, and you ass has become extremely dry or chaffed.
2)The feeling of having wiped with pine straw.
Cave man 1: Why is Bob walking funny?
Cave man 2: Oh, he has diarrhea and he ran out of leaves so he had to use pine straw to wipe, so he has Cave Ass.
Cave man 1: HAHAHA!