Definitely sexist as there was no way a girl would have been asked to do the same. I had almost wiped the incident from my mind but this discussion brought it back. I would not have told my mother as I would have received no sympathy – she was very scathing about what she called “mock modesty”. I do not recall any teasing from my classmates later – it was a happy class and our normal (male) teacher was excellent.
As for bullying in change rooms, I do not remember that at all, though one PE teacher followed the long, sad tradition of bullying the fat boy and some other boys took their cue from him. I do remember rushing to get changed. One PE teacher had a short thick “hurry-up” stick to chase us out of the showers, but far more effective was the petite female teacher who threatened to come in if we were not out in 3 minutes. She taught English but was standing in as the PE teacher was sick.