A complete asshole. Someone who you want to highfive. In the face. With a chair.
Usually following the word "little."
"I think Bryan18 from Urban Dictionary should go to hell."
"I agree, he's such a little fuckface!"
Abbreviated as HFY occasionally, this phrase means "Yes," but in a way that is either expressing extreme excitement, Happiness, or agreement.
"Dude, wanna go to a concert with me tonight?"
"Hell Fucking Yes!"