Hm... that's a good question. What determines a persons taste in music...
I think it could range from what you grew up with, to what your older brother/sister listens to. Sorta of like a "tag-along little sibling" thing. Or even the people you surround your self with. Most of us are in High school, some in middle school, so I think its safe to say that about 80% of your school's populace is all about the more mainstream stuff which usually means its almost unique to have a serious taste in other music.
My best friend and I both play guitar making it very common to have a unique taste in music (if you play any kind "Rock" instrument you tend to listen to bands for obvious reasons). He's a serious hard rock/class rock/guitar rift kinda guy. Rush, Metallica, Steve Vai, those types. Although I'm more about the modern bands. rock/pop-punk/alternative types bands like Blink-182, AvA, Yellowcard, and The Killers. So we have some common interest. Both of us share dislike in all the Modern crap. Some people have a strange array of taste though. Like I'm close friends with this girl who is a total Taylor Swift type "Country Girl" but loves all the main stream stuff. Yet she hates all the stuff I listen to because its "loud with guitars and stupid" as she puts it.