Funny, when I was working in the fast food industry in high school, it was usually DUmmies that would come in and try the cheapskate shit like eating most of a meal/pizza/whatever and claiming it was bad, being total dicks about their order, wanting specials that no longer existed, etc.
And yet despite it all, it wasn't so bad as long as the manager wasn't being a dick. Although we had one at a pizza place I worked who would take the phone, go into the reefer (cord still attached) and talk to her boyfriend for HOURS (literally) at a time. General manager didn't give a shit about her, but woe be unto you if he saw you slowing down at all. She didn't last too long after people started unplugging the phone when she was in the reefer. She'd come out all pissy, demanding to know who disconnected her, whereupon we'd say, "Well then, why don't you complain to XXX?"
Oh yeah--we were allowed to split a medium pizza between two people each shift. Another guy and I PILED so much shit on our pizza one night it took three times through the oven to get it all cooked. Neither of us finished more than a slice and a half.