I'd worry about someone who mistreats waiters for the simple reason that it is a sign that person is a complete idiot. Unless all that's left is for the waiter to bring the check, you are pissing off someone who is going to be handling your food. Mistreating the waiter is just asking for the next dish to be seasoned with spit or worse.
Depends on the country. There are still places where being a waiter can be a career but if you get caught doing something insane like that (I personally think spitting in someone's food should be a crime on the level of assault at least) your career is over.
