As has been mentioned, a way of agreeing with something, but I always found it to be almost condescending (in a cool way.) It seems like a "grown-up" way of saying "duh" almost.
Something Jayne Cobb from the popular TV show Firefly would say if someone told him how awesome his hat was.
Kaylee: I think it's the sweetest thing ever.
Wash: A man walks down the street in that hat, people know he's not afraid of anything.
Jayne: Damn straight.
