If the service is poor, .01 to 15% depending on if it is really the servers fault or if the kitchen fucks it up. BUT i have had some horrible service, no drinks, no refills, food comes out cold. or i order steak and ask for it rare and it comes out well done. and the server never asks about the steak. then it gets into the pennies, regardless how much the bill was, and they are lucky i dont ask to speak to the manager. because i can be a prick. generally im laid back though. but if i shell out a c note or more then i expect some good service.