adj. The act of hitting one's face with the palm of one's hand to signify that explaining how stupid what was just said or done (in words) JUST DOESN'T WORK!!!
N/B When additionally something as stupid or stupider is said while you are facepalming, you are socially required to do a rare 'double facepalm,' wherein the subject (you) hits the back of their first hand with the palm of the other
N/B/N/B There cannot be a triple facepalm, when such a thing is required, decapitate the offender with your teeth
*subject one: "dude, I just tagged you on MyBook"
*subject two: *facepalm*
*subject one: " Wait, no, it's FaceSpace isn't it?"
*subject two: *double facepalm* "Ow, my face!"
*subject one: " Do you need a healthpack man?"
*subject two: "Triple facepalm."
*subject one: *facepalm* "Dude, it just doesn't work!"