shitup
A common prank resulting in the victim attempting a blind-folded situp and encountering the perpetrator’s ass at the apex of the situp.
Bart wanted to impress his friends with his ability to achieve at least one situp while resisting the force of a towel pinning his head to the ground by a buddy. Before he knew it, his nose was cheek deep in ass and he realized he had actually performed a shitup.