lol i thought it was pretty commonly known
donkey punch- definition from urban dictionary
Verb. Noun.
Whilst participating in either vaginal or anal ‘doggy style’ intercourse, during the instant before the male ejaculates, the penis is inserted (or kept) in the female's anus, at which point he delivers a swift punch to the back of the female’s cranium. This results in the simultaneous contraction of the anal sphincter and various other muscles in the female, thus producing a tremendous sensation for the male. However, for the technique to render successful, the receiving party must be knocked utterly unconscious.
i do believe this has been done in one main stream porno before