i'm a discriminatory tipper for sure, because i've spent over a decade busting my ass serving people, and i know what a very hard job it is. i don't think a lot of people who haven't done it for a living realize that, but i also don't think it takes much thought to consider it. there are a lot of extenuating circumstances that some people don't take into consideration...like the kitchen. i've worked in places where the kitchen staff sucked so bad, it was like pulling teeth to get the food from them, and when you did, it was of extremely poor quality. some people jump at the chance to take that out on the server, and out of the server's tip, when in fact, it was not the server's fault, and the server had been in the kitchen ripping the cooks a new asshole in defense of the customer and their tip.
when i dine out, i make sure i watch the server. i take a look around and consider how busy they are, if there is some asshole customer monopolizing their time and effort. there have been situations plenty of times when i was so slammed with customers that i was running my ass off trying to do the very best i could, and still couldn't give everyone the service and attention i would have liked to. that is not the server's fault. i have also waited on one table that was so needy and picky that they demanded more attention than the entire rest of my station put together. i learned not to pay so much attention to those needy tables. some people are just sociopaths and don't deserve the privilege of being served. that's not the server's fault either.
but i've also had servers that showed unexplained animosity and apathy. i've watched them idle and neglecting their responsibilities, and i don't think those servers should make nearly as much money as those who exert an effort and do a good job.
bottom line...when i dine out, i EXPECT to pay a gratuity of about 20%. if i get service that is REALLY good, i've been known to leave way more than that, and if i get service that's REALLY bad, i've been known to leave less than that. but i know from being in the industry, that some people are looking for a way out of paying for the service they receive, and if they're looking hard enough, they'll come up with one. it used to make my laugh...those customers are easy to spot as soon as you walk up to the table. i'd bend over backwards to give them impeccable service and watch them get more and more pissed off because they couldn't find anything to bitch about. and in the end, they wouldn't leave a tip anyway...they never planned to. i made sure they knew that it didn't have a damn thing to do with the service, and that it was just a matter of them being a selfish asshole.