When a male is having sex with a female in the doggy position, and the male is about to cum he sticks his finger up her but and when she turns around to ask what the fuck he quickly pulls it out and cums in her eye.
When you surprise someone with a variation on a Wet Willy ... but instead of wetting your finger with your mouth, you wet it with your butt. And instead of putting it in their ear, you put it in their mouth.
While making love doggy style, you stick 2 fingers in her asshole. Then remove the fingers and reach around to her face, in one swipe wipe her upper lip with your index finger "Dirty Sanchez". With your middle finger simultaniously hook the inside of her cheek "Fish Hook".
A close relative of the "shocker," however, it differs in technique and execution. Invert your hand and direct two fingers into the stink box, immeditaely followed by a thumb-hook to the stinker. You can also perform a "hooking" motion (like your twisting open a can) for the full effect.