This just in.
“Face palm” seems to be the new It Girl of cool expressions. This phrase refers to an act of stupidity. Today, I even saw “double face palm.” Presumably, this expression is twice as cool. The action itself of hitting one’s forehead in this manner has been around for a long time. But the Urban Dictionary‘s listing that notes that a speaker actually says “Face palm” rather than literally palming his face, was only added on 10/31/10.