The way that people treat you as a server has complete control over how you act as a server. When you have a table that is being nice, polite and patient with you it makes you want to go out of your way to make them have an enjoyable experience. I LOVE serving tables that are polite to me and friendly and want to talk and are just nice people. I really do. Even if they leave a tip smaller than I'd like.
However when you have a table that is being demanding, rude and needy. It's really frustrating and not only does it make you short with that table it puts you in a not as good mood and it rubs off on other tables too.
I would much rather serve a nice table, that is being friendly and fun and receive a poor tip from them than to serve a rude table and get a better tip. It really changes your mood for the night. Just the one rude table can really bring down your night.
Remember that the next time you go to a restaurant, servers are people too, and while our job is to serve you, we do like to be treated like people and if you treat us kindly and with respect and our friendly with us you will have a lot better experience. I remember the tables that make me laugh and were just tables that I genuinely enjoyed taking care of :)