chump-humpin'

When an unfamiliar guy (a.k.a. "chump") comes up behind a woman on the dance floor and starts grinding away on her behind, waving to his buddies, getting off on the fact that he'd never be able to get this close otherwise...

"Lisa, I gotta get off this dance floor - there's this guy that's been chump-humpin' on me all night and he's creepin' me out!!"