20% minimum no matter how the service was. Increase from there if you think they did exceptionally well.
You've got to be kidding me. There ain't no way in hell I'm leaving a tip for bad service. No way in the world. I refuse to give my hard earned money to someone who doesn't deserve it.
If my waiter was nice and gave me good service I generally leave $5 for a tip or I'll use the tip calculator on my phone. If they were working a lot of tables and they weren't as attentive as they should be, then I would let it slide. But if the service was poor and the waiter was horrible they would get not one red cent. Though, I do like the idea of leaving a penny.


