Most people who leave a bad tip for good service have never worked in the food service industry. They really have NO clue as to what a server goes through to make a dinning experience perfect.
If the chef is slow, the server gets the brunt of complaints. If the host sat them in a bad spot, the server hears about it first. If the food sucked, the server has to apologize and work out a deal.
When I eat out, tips are 15 to 20% for average good service, 35% for super great service and the rare 50% for the server from heaven. For the bad server who is lazy, never smiles and is mean to the kitchen staff, they get a tip written on a napkin. The last tip I wrote on a napkin was: Never accept wooden nickles from a Camel.
If you like to dine out and can not tip too much in money then be creative. When I was in college and waiting tables, I received tips that were part cash and part: bottles of really nice wine, a massage certificate to local spa, free prepaid tasting card from domain chandon, movie production tee shirts and hats, certificate for a resume make over, buds, haircuts, free dinners at other restaurants, coffee cards from Starbucks.