This means "You sure do shake your damn head alot." Was found on the definition of 'SMDH' Aka:"Shaking my Damn head."
Guy: "Wow I'm so in love with this chick, OH I MEAN CHICKEN YEAH I MEANT CHICKEN"
(Instead of face palming you could say:)
(And He'll say:)
(Thats when you facepalm.)