A theoretical fold of mucous membrane occluding the rectum. This structure is only present in anal virgins, and is broken upon anal penetration.
Anal counterpart to the hymen.
Hell yeah he's a player - he broke my butt hymen after our second date.
This man's butt hymen is ruptured! Call a doctor!
getting fucked in the ass for the first time
joe "dude she cryed when i stuck it in her asshole"
John "must have taken her butt hymen"