Hungry, hurried people are hungry, hurried people, and human service is human service. The fast food tradition is that neither side much upholds their responsibility in the bargain. i've met plenty of people unfairly nasty to workers, but then i've also met workers whose idea of good service is to pile pickles on a no-pickle order. Or to make sure ketchup-only is truly ketchup-only.
But as a fast food clerk, you are paid to put up with the public.
EDIT: Oh, and the thing i hate most about fast food is that it sucks.