I don't think I've ever not tipped a server. The only time I would probably be if I had absolutely horrible service.

I tip minimally $3 even if 20% is like $2. I don't go above 20% really but I will very rarely tip 10% or 15% if the server is rude, etc. I get you make your living off of tips so I will tip but if you're a rampant asshole I'm not going to tip you the full 20%.