A grebo is a commonly used term for people who follow an 'anti-pop' culture. The grebo's archenemy is the townie; grebos generally prefer to wear baggy, darker clothing as well as simple metal jewelry to reflect their darker, anti-pop lifestyle. Most grebos will listen to Slipknot or any other number of popular nümetal bands such as Disturbed.
The contradiction of the Grebo is that through their anti-pop mantra they have effectively created a subculture much like the one that they have rebelled against; it is one that exists to defy the opposite of what pop culture is, and still has its own subcultural standards in wardrobe, music, speech, etc., making the Grebo subculture somewhat pretentious, yet more open to social outcasts or socially unaccepted / otherwise politically incorrect schools of thought or action.
Look at those Grebos, listening to Slipknot. Don't they see that through their rebellion they have built nothing much greater than the culture they have rebelled against?