My wife used to wait table at Olive Garden before we were married.
She had one regular that would ask for her and insist on being set in a booth during dinner (busy) time (by himself), order only a coffee, insist of free biscotti, stay in the booth for 2-3 hours, and tip a nickel if anything at all. Sure, he only spent $2, but he routinely got $5 of free biscotti with his meal.
If he had not been sitting there, she would probably have had two families of four through there in three hours and made $20 - $40 in tips off of them.
She also loved the people who let their young children run free through the restaurant--often causing wait staff to drop whole tables worth of meals as they ran in front of them.
Then there was the guy who would get there at 4:30 for dinner and park his Jaguar sideways across three parking spaces. He would scream at the hostess if
his table was being used--apparently it was supposed to be kept open at all times in case he decided to drop by. He would always find something wrong with his meal, always demand to see the manager, always get his meal comped, and always stiff the wait staff.