Great point Brad.. It's like road rage. Cutting someone off because they cut you off doesn't solve anything. It might make you feel good for a second, but it just leads to more road rage.
Giving poor service to these people is just reinforcing the fact to them that they shouldn't have to tip good, because they always get crappy service anyway. What if you gave crappy service to someone and they left you a big tip because they believed it was the right thing to do? How would you make that up? Would you expect a good tip next time they visit and sit in your section?