uglies bumpin' uglies

Refers to the phenomenon of two extremely unattractive people having sexual intercourse.

Person 1: Wow! Your neighbors, the husband and wife pair, sure are ugly.
Person 2: Yes, they are. And, guess what? The walls are so thin in this place that I heard them having sex last night.
Person 1: Ugh! The sound of "uglies bumpin' uglies" brings terrible images to mind. Awful!