Caleb,
You nearly had my sympathy then, until that admission about metal
. Actually I used to get into Purple, Sabbath etc until some (6-12month) older and wiser astronomers turned me onto Yes, Crimso, early Floyd etc. And the hair length didn't have to change!
The problem you have is of course very common; I even recall seeing footage of the Beatles being told to get a haircut, and they were only mop-tops at the time.
In my case they wanted about 3/4 of the male student population to get a haircut (and about the same proportion of the female cohort to get a longer skirt). The weight of numbers of course gave us a great advantage. It was impossible to punish that many miscreants at the same time and if they tried to pick you off in small groups it would be years before your turn came around. So, is it only you or do you have allies? You can try the 'why should I when his is so long?' line. Also, what real leverage do they have? I certainly wouldn't miss any school over the issue but I might have tolerated some lesser punishments. Also, where do your parents stand? I actually copped it worse at home than at school (boy could mum nag), but my parents wouldn't have supported any 'over the top' punishment. I also kept some heat off me by being academically pretty good and otherwise well behaved.
So how much longer do you have to put up with the hassle? Probably looks like a long time to you but nearly nothing to us more senior contributors
. After that you'll be free to grow it as long as you want for as long as you want. That likely means about 10 years. By then you will find it /too hard to care for/always in the way/a disaster on windy days/too hot in summer/a pain in bed/ and get it cut of your own free will. Such is life.