Calling someone a "Nathan Barley" means there a bit of a c*nt to put it simply. There waste there money of independent expensive trendy clothes, ONLY listen to underground music, attempt to imitate "Banksy" (See Banksy) and think there the king of urban "cool" (Just like the Nathan Barley from the show.)
East London is the spawning point of "Nathan Barleys."
Nathan Barley is a fictional character that represents all that is bad about the Shoreditch twat, a rich middle-class white guy of a wank stain, schooled in the arts, who thinks they will revolutionise the Internet and wear the coolest 'alternative' fashion clothes, and hang out in the coolest places of East London. In reality, they are out of touch, sheltered, self-absorbed guys with laughable 'trendy' haircuts and generally regarded as cunts by anyone whose ever met them.