When somebody puts their eye as close to your ass as they can and you fart into it.
Guy: can you check to see if I have a hemorrhoid?
Girl: I don't see one
Guy: Look close I really think I have one (farts into girls eye)
Girl: I'm going to get pinkeye from that butterfly ass kiss!
6๐ 8๐
When a girl is wearing leggings / tight trousers and her underwear cuts into her ass cheeks causing 4 defined buttocks (butterfly ass)
Kevin: โOmg did you see that girls butterfly ass, she really needs to invest in some thongsโ
Lance: โtoo right my guy, that ass is butterfliedโ