When a person is so large, so huge, just basically a fat ass that is so bizarrely BIG that their genital area is increased in size, it is increased so that it looks like your vagina has been blown up like an inflatable mattress and now looks like you have two butts: your ass, and the butt located at your private parts.
This occurs when a person with a rather large gut seems to think that pulling his/her trousers up over the projecting gut improves their look. Thus giving them the appearance of having personal front and side air bags.