For that matter, fuck self-riteous waitstaff who think they can determine what percentage of my food bill should be donated to them. I will punch you in the fucking face. There's your tip. The rules are:

If the service was good and prompt the rule of thumb is to tip 15 percent.
If the service was very good, leave 18 percent, and if it was extraordinary, leave 20 percent.
If the service was only fair, tip less, from 10 percent to 14 percent.
If the meal was appalling and the service abysmal, anything one feels like leaving will do.

I'm generally leaning toward the 20%, but if you mention the paucity of a generous tip, I will fuck you up. I'm going to start my own wave of pamphleting broadcasting a new message: "Waiters love ass pennies!"