Go the rabbit punch.
When you've finished you just smac them at the base of the neck as hard as you can. Causes the sphincter to tighten as much as possible and they jerk forward scraping as much of their sloppy arse shit off as possible.
SG
You mean "donkey punch"?
Ok, yes, for that it's traditionally done during vaginal sex, just before the guy finishes he pulls out and sticks up up her anus, simultaneously hitting her on the back of the head/neck, preferrably hard enough to render her unconscious.
Apparently people actually do that, and various women have ended up with brain damage as a result.