Sexual intercourse involving the use of a penis. Not a fake penis, but a real penis possesed by a male of the species. e.g. a lesbian cannot "penis" another lesbian.
Often used when defeating another player in video games. Made popular by players in halo 3 who would often change their symbol to a grenade and a banner. This when changed to one color (commonly red- got raped so hard there was blood) look a lot like a penis.