People all over play favorites - this is not some demonstrable symptom of gender discrimination.

That's an opportunity issue. You can't prove that they would have been paid less for the same work. And there might have been other reasons why he wouldn't let them.

That's your side of the story in one particular case. It hardly constitutes empirical evidence. I worked in a store where I rose to a supervisory position. I was never accused of favoritism or unfair treatment or anything remotely like that, but a female fellow supervisor once told me when we were co-in-charge of a very busy holiday shift that she would take care of directly supervising our subordinates and leave me the paperwork in the office, "because you make the girls cry." I never once shouted at an employee, called them names or insulted anyone, and the closest I came to an accusation of sexism was when I put dry ice in a toilet bowl, and a woman happened to use it next. The only fault anyone dared to accuse me of in that scenario was not being more gentle or nicer to the female employees. Sexism goes both ways. We had single mothers and single fathers working there. Guess which was the only gender given slack on attendance issues related to their kids? I worked in a Burger King in high school, and all the male employees were relegated to the kitchen, and the girls were the only ones permitted behind the registers and to put together orders. It had nothing to do with seniority, as that was another job where I rose to the top seniority-wise by virtue of reliability. The only jobs we were ever allowed out of the kitchen for, were taking out garbage, mopping the dining room, cleaning the bathrooms or policing the parking lot. The girls were only sent to the kitchen if there were not enough male employees, and the guys were NEVER permitted on the register or service stations. If there were no customers adn the countertop was clean, the girls were allowed to lounge around by the registers and chat. In the back, at the same time, the boys were being yelled at to mop the floor whether it needed it or not, stock this, slack that, sort those, etc. etc. If it got too slow and they decided they did not need the whole crew, it was always a guy who got sent home and shorted on the hours.
Don't give me any crap about females being discriminated against.