My brother is a waiter, so I'm well versed in the daily frustrations, the hard work, and the kind of shitty "Mr. Pinks" out there, so I always make sure to tip at least twenty percent when I'm out, at the bare minimum. Barring one egregiously bad encounter at a bar in my hometown about two years ago, I've never strayed from this pattern. And even then, when I discovered that the waitress at that bar had actually gone and adjusted my tip on the receipt in her favor, I ultimately let it go. Yes, it was really awful service (she spent most of our time there conversing with her friends, and almost ignoring our table) but at the end of the day, it was just a couple of dollars, and I didn't really feel like it was worth the hassle or the trouble to correct.