its a person that has a saggy ass like a diaper nd its shaped like one
Hoe: Hey daddy you like ma ass
Pimp: Hell no bitch you got dat Diaper booty
A girl with flat butt that has a little sag to it in an unappealing manor, usually in a pair of jeans. A butt that resembles a sagging baby diper.
Man, yo girl gots Diaper Booty. or When that girl turned around, I almost ran from her Diaper Booty.