Every sub-culture eventually develops a distinct style. Those who consider themselves different from the masses are really touchy about it. It doesn't matter if it's a leather jacket or baggy pants or colored hair or body piercings or whatever... As soon as enough people do it, a new 'rebel uniform' exists. People who are not part of the sub-culture pick up on it, copy it, and it becomes a trend. The trend is then mass-marketed to others who want to show the world that they are different too.