A very fat and grossly overweight hoe, slut, bitch, whatever you'd want to call her.
One of the signs that indicate that the world's going to end soon, is waking up the next morning only to notice some ugly smothering hoepopotamus lying next to you like a beached whale and then being shocked to having realized that you've actually got her pregnant!
When a person's face is so bloated and deformed that it's impossible to distinguish it from their ass. As it is, the ass already resembles a hippopotamus face. For the poor bastard sporting one of these, it also resembles theirs. It is a synonym with "Ed Zachary Disease".
Yikes - look at that double hippopotamus. If he ate with his ass and sat on his face, I wouldn't know the difference.