I always tip at a restaurant/diner. Usually though I reserve that for places where somebody actually has to bring me drinks and food all the way from one side of the restaurant to the other to my table(Chili's, Applebee's, Weck's, Red Lobster, Outback steakhouse, Denny's, Village Inn, Twin Peaks, Hooters, etc). Don't get me wrong though, I would have no objection to a place raising their prices in order to pay for an employee's tips. Sometimes however it's kind of impractical. I mean if I'm going to a place like Panda Express or Jack in the Box, a quick tip calculation would find the tip being under a dollar, and sometimes I just don't have the change for that. Also, those places never have a tip jar so I have zero incentive to leave any kind of tip.
Tell me if this sounds stupid... judging a person based solely on their looks is just as ridiculous as the practice of phrenology.