First the man grows out a huge bush. 70's style, so if standing on your head it would look like a hasidic jew "beard/nose" combo.
Then you shave it off and place it in a ziploc bag keeping it in close proximity to the next location of sexual promiscuity.
So the next time you're barebacking a chick from behind pull out just in time to unleash your jizzum all over the female buttocks.

Quickly grab the ziploc and dump contents all over said jizzum. wipe it in nice and good then jump on her back with enough forward momentum that your propelled off the bed on your makeshift flying broom (nimbus 2000)

One who has a mania for music.

The Harry Potter (n. & v.):

Occurs when, during a three-some, a female is jacking off a male. Right before he's ready to culminate, she yells "Alakazam," quickly turns the cock and, in a wand-like motion, yanks it so it blows all over the third member.

When you're doing a girl, have a friend hide in a closet. Then, when you finish, he jumps out and yells "TEN POINTS FOR GRYFFINDOR!!!"

Optional: Friend dresses in formal wizard attire.

A man jerks off and then, using the semen that has accumulated on the tip of his dick, draws a lightning bolt on his partner's forehead.

After which he kills the recipient's parents, or next of kin.

before a guy and girl have sex a friend hides in the closet in a wizard costume when the guy and girl are doing it or after the fried proceeds out of the closet and screams 10 points for griffindor and then runs out