I deliver pizzas part-time, and have noticed that people in the richer neighborhoods don't usually tip worth a damn, and usually the big tippers are people who don't seem like they would be good tippers, based on how I perceive their financial situation to be.
I don't know why this is, or if anyone else has noticed this. Maybe the people who have lots of money have lots of money because they are stingy with it
I usually try to not let it bother me when I don't get a tip. I figure if I have a bad attitude towards them, then I have just lowered myself to their level!