Here's a list of bizarre things that my school in Belgium was intolerant about back when I was in school. These are just the ones that come to mind right now, there were many others.
1. No short hair for girls. No bald boys. No dyed hair.
2. No piercings for boys, and only pierced ears for girls
3. No hats. No shorts.
4. No long skirts for girls. No short skirts for girls. Only between knee and calf length or some such bizarre nonsense.
5. No skirts for boys (I tried a kilt once, was not appreciated).
6. No rings for boys. Not "too many" rings for girls.
7. No sitting in boys' laps. Except when you're a girl sitting in another girl's lap, that was apparently fine.
8. No tops with straps thinner than a finger (for girls, I guess).
The problematic gendering aside, all of those rules always seemed bizarre and stupidly specific to me. Did a pierced bald boy with a ring once torch a school? Do teachers have some kind of phobia for specific hairdos? I get that it's a conformity thing, but conformity never struck me as being useful.