Perhaps the waitress should work on improving the level of her service.
95% of the times when you get bad services from a waiter or waitress it is due to things out of their control.
I was a waiter in college and one day, 2 of the other servers called in sick at the last minute. Managers helped some but I was waiting twice the tables I normally do. Another time a line cook went home for an emergency so people waited longer than normal for their food.
I always tip even if services is slow...and I can tell a incompetant waiter.
If I was dictator every person would have to be in food service for at least 6 months to get a taste of it. Lot's of idiot customers out there.