Why do modern day teenagers take themselves SO seriously? And treat people who are different like crap?

I'm nearly 15. I'm a girl. I spend my free time usally in my attic room, and I've covered like EVERY bit of wall up with music posters and rip outs, it looks awesome. I don't drink or do drugs, I live on coffee.. I usally just draw cartoons or chat online when I'm at home, I never leave my room. When I go out I sit around the Skatepark with some of my friends. I sometimes go shopping and go to Starbucks. At school, people just treat me like sh*t. I'm not really bothered with all this mainstream stuff, I listen to The Misfits, The Pistols, Nirvana, Blink 182 and the Cure mostly, and people critise me for that. It just annoys me. I like being different I guess but I just dont understand high school at all -.- It only brings misery, I hate what it does to me. Everyone cares about themselves so much, I just don't fit in with the other girls at all. I just dont fit in anyware, most of my friends bunk off school most days, but I actully want to go somewhere in life so I dont. Thing is, I probably want to be a musican or something but I may as well try my best in High School right? I'm in relativly high cles. I dont dress like the other boys and girls, I usally wear combat pants and a band shirt and trainers, I'm not too bothered about how I dress. I dont see how the other guys and girls care about their image so much but I dont critize them for it, I'm quiet but friendly most of the time. I just dont understand, I cant escape the feeling I dont fit in anywhere. I dont get all this popluar stuff at school, why do people get intimdated by them so much? Their all horrible and nobody really likes them. And what is it with girls and being so bit*hy? I dont talk mean things about anyone, let alone MY FRIENDS? I dont understand modern teenagers at all, I just dont get it, why do they all have tight pants and wear neon shirts and neon sungles? At school most of the time people just ignore me. Does todays world confuse anyone else here?! >.<