all a guaranteed tip of 18% for a table of six guarantees is crappy service....
Not from my experience. Whenever my family goes out, we receive excellent service. Big parties tend to tip above the 18% when the service is really good, and the wait staff knows this. And knowing that there are plenty of people out there who will stiff the wait staff, I don't blame them for adding the gratuity to the bill for large parties.
My girlfriend is one of those who doesn't believe in tipping. The first time she picked up the tab, she tried leaving a $3 tip on a $45 order. The service was decent and there was no reason to be so cheap. I read her the riot act. She's finally coming around and now will leave 15%. I usually add a few bucks if she's paying. And yea, she's got money. It's sometimes surprising who will tip and who will not.
That being said, if service is truly crappy, then a customer does have the right to refuse to tip. Funny thing is that management will almost always acknowledge poor service, so something about this story sounds fishy to me. If a restaurant is extremely busy, and the food is slow coming out of the kitchen, that is not the server's fault.
And if you want to know who the worst tippers are, it is Blacks. I still haven't figured out if they it is a racist thing with them, or if they are just too stupid to know better. And yes, some Blacks do tip very well, but they are the exception. Many of them don't tip at all. Second worst on the list are Indians from India. With them it is simply a matter of being cheap. They expect something for nothing. After them come the Jews. They will usually tip but not much. On the other end, Arabs tend to tip very well.