The strange anatomical phenomenon that occurs when a woman's breasts don't quite touch each other. Quite a turnoff, generally.
Luke: I almost went all the way last night with her, man.
Gregg: What do you mean "almost"?
Luke: Well, she took her top off, and then I saw the space between...
Gregg: Oh, man, gross.
Luke: Yeah, and then that awful Dave Matthews Band song popped into my head, and it was all over.