5% if the service was absolutely horrible and they just werent doing their job.
20% if they did their job, but they were busy, and I know they couldnt get to me in time to fill drinks on the spot of whatever
25% if the service was the least bit impressive
30% if they did an outstanding Job
Then if they made me leave the restaurant, or I decide I'll never go back because of the service, Then I dont tip anything to make a statement, and I'll probably tell the manager why.