As the mother of a 13 year old, I'd like to contribute "scene".

In other words, if a band used to be really underground and cutting-edge, but now they've gone mainstream and get lots of radio airplay, they're "scene". "Scene" can also mean a poseur: somebody who dresses in a particular non-mainstream style but who isn't perceived to walk the walk, and listens to the mainstream bands instead of the real, proper, cutting-edge ones.

example: "Look at her. She thinks she's SOOOO Emo in her stripey socks and her eyeliner, but she listens to MyChem and Fallout Boy. She's so scene."

This will usually be followed by a group of the accusor's friends shouting "Scene! Scene!" at the accused from across the road, which may be followed by a standoff between the Emos and the Scenes, before they all repair happily to Subway or McDonald's to drink coffee and look bored.

And that, my friends, is youth culture in Britain 2007.