I'm female so never told to cut my hair but at school I was made to tie it back, even though other girls didn't have to, because some of the teachers decided my hair was too big/unruly. That surely must be discrimination against people with naturally big hair?!
Either way, just play the discrimination card if someone tries to enforce something and tell everyone else to f**k off.
However, I do like to offer a balanced argument so it's also worth mentioning that change can be liberating, pushing you out of your comfort zone and giving you more confidence as a result.