Mom and Dad always taught me if you can't afford the tip you can't afford the meal. We tip %18-20+
This. My mother was a server my entire life and I would never not leave a tip. Even at a buffet, a server does a lot(and like with basically all restaurants there are probably things they do that you don't see) and for significantly less than minimum wage. They rely on tips to make their living and to deny them that because you(general you) are cheap is just wrong.