He can wear whatever the **** he wants, who are other people to determinate what kind of things he has to wear, it doesn't matter if it looks stupid or not, he has the right, as long as it don't make damage to other people and himself!
Lol tying his shoelaces will make damage tho.
I know that he can do whatever he wants but there are still certain limitations especially that he is still a teenager and you go to school to study and not to show off. I think the school did the right thing as it was ****ing inappropriate. He can do his hair like that after graduating but since he's still in school there are certain policies he (and other children) should follow and it's really a no brainer for the school to ban that.