The subtle act of pleasuring one's self (male members only) through inserting the tip into a door jamb, or other hinged objects, and then proceeding to slam said object aginst the tip thus making it bleed. This results in not only immense extreme pleasure, but also a lovely indoor fireworks display of man magma, a name derived from the appearance of blood stained jism.
Man 1 : Holy good wank! what happened to yer nob?
Man 2 : I had the mother of all power wanks last night
Man 3 : No shit.