What's the stupidest rule your school ever enforced?

It's not enforced by my schools, but when I was little, speaking local languages at school was forbidden. It's getting better now, but at that time, only the official language was allowed.

Another rule was boys weren't allowed to wear longer hairs. If the hairline was below the ears, they would be asked to cut it shorter. From time to time, boys from my class were forced to cut their hair during classes with the company of a teacher.