As a person who used to bartend professionally, I find your assertions categorically unlikely, especially if the places you
claim bad service is in popular venues and clubs.
For starters, owners of these bars and clubs make one thing very clear to every employee: women get preference. Why? Because if there are no women in a popular club, there will be no men. The reasons for this should be clear to anyone, so if a patron complained they received poor service because of her sex, the offending server would be out the door.
Also, your broad assumption that bartenders only see potential tips when they decide on who they should serve next reveals a keen misunderstanding about club bartending: it's not a restaurant, where a relationship exists between server and patron. A club bar is a little more than a hip feeding trough. You shout your order, you get your drink, and you pay. Most bartenders don't even stop to consider who tips them, let alone if they feel they've been stiffed. Why? Because bartenders are very, very busy. They have no time to be worried about bad tippers.
A club is a very different place behind the bar: you don't see people as individuals. You are trying to serve dozens, if not hundreds of people simultaneously. You look for clues: does that person have cash in hand, ready to pay? They get preference. Is that person being a pushy jerk, yelling out his order when he knows I'm not ready to serve him? He isn't getting served, at least not by me, in any sort of timely fashion.
It's studies like these that make professional work in the service industry even more demeaning than it already is: poorly crafted, scientifically dubious
surveys that do nothing but feed some dated notion of victimhood in the service industry.