In response to Mike-J-D's comment:
OK if that's the case at Pizza Hut, they have sitdown tables there as well, where a waiter will serve you like any other restaurant. Are you saying they aren't expecting me to tip if I would have ordered and eaten it there? Of course they would, and I would have tipped. Because I'd be tipping on the service I received.
I'm not saying don't tip at all. And I have never not tipped. I hear a lot of ex servers say everyone "should" tip 20% regardless of service. Which I disagree with and I think that is what a couple others here disagree with.
Another example. I was out to dinner with my girlfriend about a month ago. She used to be a server too. it was a sparse Wednesday evening crowd but the service we got was inattentive, slow, the guy seemed disinteresed, had poor body language, honestly acted like we were inconveniencing him by being there. She even said to me "I don't think he likes us". We both agreed the serivce was terrible. Are you saying this guy deserved a 20% tip? No way. The guy deserved $3 maximum (on approx. a $25-30 bill) in my book. Although I tipped more because she asked me to,being a former server. Not as much as she would have though. It isn't about being cheap, it's about giving a tip based on the service you receive.
That's a different story. Now they aren't just handing you a pizza they are providing a service to get you drinks, refill your drinks, serve your food to you after, and clean up after you are done. That's much different than ordering a couple pizzas for take out and them just handing them to you.
As for the 20% I generally give 20% for even average service but if a person is really bad (as you described) I will give the 12% to cover the assumed tax on the tip and nothing more. I think we all said you tip on service provided but it goes both ways and you shouldn't not tip or tip low because you order the $30 steak instead of the $7 salad.