When I was a waiter most people were very forgiving and nice. I even remember a group of old ladies from Yorkshire who came for breakfast each morning and requested me and wanted to know which days I was working mornings. They were funny and would quiz me about the surrounding area. Management really didn't care what I was doing, but I found being personable made MY day go faster, and kept my mood up.
Though yeah, some real nasty folks out there. For instance, if someone wanted tea, I had to use the tea machine in the kitchen. I brought a guy a pot of tea and he was BALLISTIC at me, said the tea was cold and I should get him a fresh one. So I went back to the machine, made sure the water was hot and gave him it again. He threw another hissy fit at me, I apologised and said I would make him a pot myself. So I had to use a regular non-industrial kettle in the kitchen and make this guy his pot of tea while also trying to tend to about 10 other tables.
The other people at his table though tried to talk him down, saying the tea was warm and it isn't a big deal, but the guy wasn't having any of it. Ugh. Tramatic memory. Worst thing is it was my first job and I am NOT used to being spoken to like that, so for a few days afterwards I thought I had done something wrong.