rump bump means that when a man grabs a woman/man by his/her hips and shoves his hard erect penis into her ass crack, while in the process of pulling his/her pants down. then, they shove the person on the ground, get on top of the person and rides them like a pony, then you go 69 on their ass
damn bitch, i had sonia over last night and i tried to rump bump her ass but it was too flat and nasty, and she was terrible.
damn hoe, i had m&b in bed last night, they were the best rump bumpers i know.
When two people bump butts, sans trousers.
Only real best friends Rump Bump