The Def. for facepalm is....... an act of idiocy that result in action as your hand completely pwn your face as you realize, you just fucked up. It's mostly common when playing Smash bros brawl.
Two people playing Smash Bros Brawl Guy1: *Dies*, FacePalm Fuck (*Release FacePalm*) I forgot i had a jump left! Girl1: AHH..HA, I PWNED you.