A couple of weeks ago, on one of the nights that was just terrible for me, other people were having an equally bad time. One of the closers had a table that was occupying three six-seater booths. It was a little girl's birthday, so they had a big group and were having a good time. The kids were darting back and forth everywhere, the adults weren't really paying attention to them. All the employees got together to sing for the little girl, who just loved it. All sixteen people were loud, yelling back and forth between tables, and generally being a pain in the ass.
When they left after a couple of hours, there was stuff smeared all over the tables, appetizer plates everywhere, gift wrap on the floor and under the tables, confetti tossed around, and generally just a huge mess.
Notice what's not there? Yep, not a red cent for a tip. This is why there's a stereotype about yuppies, or Hispanic people, or rednecks, or old people, or any other group. Not because it's always true, but because some people reinforce it.