A statement or action that leads one to perform a facepalm.
Person A: "So, how hot is that new TA in Calc?"
Person B: "Let's just say she's generous with her curves."
Ignorant Bystander: "Yeah, I really shouldn't have done that well on that exam as I actually did. Question 6 nearly killed me."
Person A (to B): "Dear God, was that ever a facepalmer."