There's a new Taco Bell commercial in which a guy talks another guy out of telling a cashier to keep the change, because he can theoretically use that change to get some new piece of crap taco or burrito or other fake mexican thing at Taco Bell. Then, as if that's not enough, as a hilarious* punch line, the guy who talked his friend out of letting the cashier keep the change hands the cashier a bill and asks for some change. If I were that cashier, I would have punched that guy right in the mouth, and I don't think anyone would blame me.
*Not actually humorous at all.