A person who creeps forward behind you at a red light, after you pull up a little, even though the light didn't change.
Jon: Hey Mike, pull up a little, let's see if that cutie behind us, bumper humps us.
Jon: Sweet, she did! She's the hottest bumper humper, I've ever been with.
Mike: Here comes the dude behind her, snap
, I thnk we started a chain reaction.