I wounder how people mean how to decide if a music is "good", or "bad"?

...On my school some of my friends starts laughing, or even mobbing me if they just see a music on my desktop that they "think" is "bad".

That is pretty annoying, because they are many and I am only one.
So when they're many they think they got right.

And they don't care if I say that people is different.

What can I do to these peoples?