We get them.
He's a regular, sort of a "Yosemite Sam" type character, wealthy, long uncombed grey hair, he's got his own private room in the back of the restaurant where he always eats. We set it up for him every day.
But some days he doesn't have a reservation and comes in to find it full.
It throws him in a rage. The thought that other people have his room, that he has to eat in the main dining room with the rest of the patrons, it's unheard of. He's curt with the staff, demanding, dismissive, not his usual patronizing self, we've given away his room, there's no placating him, the owner, he buys him drinks, pays for his dinner, and still that's not enough, he leaves without tipping or saying goodbye.
He's petulant, with occasional flashes of small mindedness.