"I'm British so I don't tip unless the service has been truly excellent (!)"
That reminds me of a scene from the movie Crash.
A guy says to another. "That waitress didn't give us good service because we're (white/black/British/whatever). She just assumed because we're (white/black/British/whatever) that we weren't going to leave a good tip."
Other guy says. "Well how much of a tip did you leave?"
Reply. "You think I'm going to leave a tip for that kind of service?"