Let me just clarify that I don't give particularly poor service to those who don't tip...I still do my job for those people, but why should I run around like a chicken with my head cut off for people who aren't appreciative and neglect those who are? That's the thing - Typically those who are appreciative are much less demanding than those who are not - The people who are not are usually out to get something for nothing, and I'm not going to be the one to contribute to that.
For example: Table 1 is notoriously known poor tippers. Table 2 is notoriously known great tippers. Both tables have low drinks. Who am I going to refill first? Table 2 of course. See what I mean? Table 1 will get their refills, but if they're not appreciative of my hard work, I'm not going out of my way to accommodate them before my great customers at Table 2.