I think DONKEY PUNCH is a good one. Also

HELM SHOT

RABBIT PUNCH (Rabbit punch is a real boxing term, when a guy gets an illegal punch to the back of the head or kidneys.)

Some other terms that would be good for porn:

BABY HARP SEAL (a helpless sweet looking whore)
CAT FOOD (same as above)
DOUBLE ELIMINATION ROUND
BROOMSTICKING
DOUBLE JUICED
BUTT SPIKE (as in, "she got butt spiked")