In work right now, I had the pleasure of actually seeing real dumb blondes D: They paid for a 17 dollar order with one 10 and one 20 because they "Like.. wanted the ten back as change." With a brow raised, I casually slid the ten out of view, then slid it back to them. They were all happy :l

EDIT
Just to clarify: They didn't want the ten broken into change or anything, they just wanted it back. As a whole ten dollar bill. I wasnt being mean or tricking them. D: