Who or what are those people who wear their jeans hanging halfway down their backside?

I can understand when black rapper types do it, because well, they do stupid stupid stuff like that, but its like every other white teen I see in the street has that sort of "style".

Half the time they're trying to pull their trousers up and the other time, you see a good portion of thier ass, which makes me feel ike a pedobear.

So given I'm old and the wrong side of 20, can someone please explain what these people are?
They're like some kind of hybrid goth, perhaps a new faction to combat the CHAV/GOTH option.

Whatever happened to just dressing normal?
I mena I never liked heavy metal people, but I still got they loved that music and wanted to show that great. Ok I can accept that.
Same goes for goths, but I still don't get the underpants thing and I don't think I ever will.

Is this just a UK thing?
Who is responsible for this.

Are you one of these people and if so what is the the deal?