People who have worked as a waiter insist that you must tip heavily for good service. The same goes for other types of service workers, like taxi drivers. Whether they are still in the profession or not, they still signal aggressively that they tip well.
But they're not the only people that act this way. I know an aspiring film major who insists on watching the credits after a movie, to show respect to the people who made the film.
This behavior is irrational. Being adamant about tipping makes you look silly, and watching the credits is a waste of time because you won't remember the names anyway. I'm not immune to it either: I used to be a lifeguard, and it has made me a stickler about rules around the pool. (The pool is supposed to be relaxing).
Why does this happen to people? I think that it's a matter of cognitive dissonance. If we work for a long time in a profession, we want our customers to act in a certain way. Then we start expressing these views (even inwardly).
When the roles are reversed and we are in the position of customer, we feel physiological pressure to match our actions with our words. This is irrational, because it leads us to weigh certain aspects of life (those relating to our work) over all others.