I'm sure someone had suggested this (Hey! There are seven pages of posts!), but sneak out and live with it afterward. Defiance of parental authority is the best!
Back in my teenage days in the late '70s and early '80s, my mom wouldn't let me have a mohawk, either. But, I went for a crewcut and the barber set the clipper for an even shorter setting. The rest of my friends thought that it looked cool and got their hair cut the same way.