Boyfriends' butt
A male's bum hole that is so loose from being pounded by another man's erect penis that when passing wind an echoing wind noise is made.
Whooosh or pheewwww or haaaaaaa or breeeebb
"Wow Tim, you have a serious case of boyfriends' butt"
"Wow Tim, you have a serious case of boyfriends' butt"