Since when is a Tip "generosity"... Giving a dollar to a homeless guy is generosity, Giving a Tip is to make sure you next drink is heavy on booze and light on mixer and faster then the last.
It is not: a tip of 15-20% is a part of the waiters salary. But anything beyond that is generosity. A $5 tip on a $9 bill may be rightfully called a very generous tip.