Would anybody care to explain this to me.?

Hmm today i had a little run in with i dont want to lable them put puck/scene girls they were saying that they hate preppy people and girls like me and they started calling me a poser because i have a small monroe piercing & small purple streak in my hair and i was in all abercrombie & fitch. they acted like they knew everything about me when i never talked to them in my life.. why does it seem people like them always are like dont judge or lable me but they go around doing it to preppy people when they dont know them? and most the time girls like that are wayyy more bitchy and obnoxious then preppy people.