I get the feeling you don't like being called a chav... thats probably why these "friends" of yours have chosen that label for you.
These people will do it more if they get the reaction they are looking for, they must be close or they would have no idea what music you play on your personal mp3 player. Its not labbeling so much but mild bullying thats the problem here.
Its easy to say ignore them, but harder to do in practise, however knowing yourself as not being a chav should be easier when reacting to there label for you.
It would be like people calling me a hippy or a gothic or even a Britney fan
I'd wonder if they even had the right person LOL
You will never find a time in your life when labelling stops, indeed as you get older it gets worse, you won't have any political or sexual labelling to any great extent yet.
What you need to find is the right reaction to it, naturally maturing helps the most so I expect (from what you write here) you'll very soon cope well with this "problem".
Just remember no matter how many times you get called a chav, it still don't mean you are one, just like it would be if these people started calling you a millionaire if you flashed your brand new Ipod at them
