To high five someone's face, usually very hard.
Guy: Oh dude woah yeah
Other guy: Totally, facefive!
I totally gave that guy a facefive.
A HARDER version of pwnage, a word said by no-one other than nerds; Runescapers, World of Warcrafters, anyone that plays multiplayer online games.
"You better watch your mouth, mister, or you're gonna get 100,000 volts of hardcore pwnage coming your way"