Fake firing
If you’ve spent any time working in the service industry, then you’ve dealt with overly-picky and annoying customers. The ones who will berate you if the meal is 2 minutes late, or if you forget to bring them a fork. Or like this one, who was picky about the temperature of his coffee.
Having been in similar situations in the past, I do like the idea of this prank, though, and I wonder if it made him think twice about having a go at a server next time, although probably not. It must have been fun to act out being fired though.