I worked at a Ruby Tuesday for many years and I can not even count how many times I got stiffed by large parties. My general tip percentage was always 20% or more, so it wasn't due to bad service. It got so bad I refused to take larger parties. All of my coworkers were in the same boat, some of them even had large parties leave nothing. I worked at a pub where gratuity was added. The customers did not mind and the servers worked just as hard on larger parties.