I wouldn't leave Burger King coupons, but if I received poor service from the waitress (that I was certain was the fault of the waitress and not someone else) and/or she had a bad attitude - I would not hestitate to leave no tip at all..
If I receive good service, I tip quite well.. However, I will not tip in places like Dunkin Donuts; McDonald's; when I pick up an order; or things of that nature.. If something is delivered, of course I will tip..