When I was a kid, my mother would often embarrass me whenever we order root beer floats by adding, "And don't forget the ice cream." Of course, the reason for that was that once she had ordered a root beer float and received only root beer. Still, I was mortified. Years later, my mother would get the same effect by tipping very badly. She had grown up during the depression--very, very poor, and often quoted a supposed expert who had written that 5% was a good tip. I became adept at supplementing the tip without her knowing.