Hump-Scumping 

A sexual act including two people, one of them male. The male stands in front of a toilet on which the other party is sitting and vomits on their head. Meanwhile, the sitting person performs fellatio on the male party and vomits on his penis.

"Those damned kids and their hump-scumping parties!"

Hump-Scumping by Walter Shmultz April 24, 2006