The Donkey Punch is when your engaged in anal sex and when your about to ejaculate you punch the poor little lady in the back of the head so her anal cavity tightens making the orgasm all that more better (for you ofcourse).

Punching someone in the back of the head may lead to serious brain damage and even death.

Donkey punching involves the male punching the sexual partner in the back of the head during anal or vaginal sex prior to orgasm, to provoke a shock causing the vaginal or anal muscles to contract around the male's penis.

The move can be prosecuted as sexual assault and even rape in the case of surprise anal penetration.

A sleazy sex move in which while the guy is taking the girl anally he punches her in the back of the head, making her ass or vagina contract.

Donkey punching is more safe and effective when you use a swift but controlled open-handed karate chop to the very base of the skull, near its insertion on the neck. I believe this stimulates nerves that contract the anal sphincter muscles.
The legal definition should be removed because the goal is not to make the recipient unconscious. Also, this is not something that people actually do, its a freaken joke, you feminazi.
But, if you were to do it, a donkey punch to the spine just above the ass would probably work better (and provoke fewer lawsuits) than a blow to the head, which might even relax the anus. This is because sacral nerve stimulation has been linked to sphincter contraction (in cats)- dont ask.
Now, if you really want to get some sphincter contraction, without the whole punching thing, you cover the recipient's nose and mouth with a hankerchief full of ground pepper or something that will make her cough (or just ask her to cough repeatedly). Coughing tightens the anus twice as much as voluntarily squeezing.

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.

While engaging in anal sex the male strikes the woman firmly and unannounced to the back of the head, this may cause an involuntary vagal nerve response of contractions most likely from both shock and the blow. this is a hard to research myth or legend that seems to have a life of its own. i think this is a poorly thought out act and potentially risky. it happened to me and i think it was the anticipatory build up that gave him the big orgasm. I had something like a dictal event.

Man of chivalry and honor, immediately precedent to Don Quixote in the fonetic fon book.