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Well spoken Public School boy who act and behaves like Chavs(townie) or people from the ghetto.

wearing smart school uniform while beatboxing and rapping.
type in youtube -

Justin Brett Stand Up at The Tricycle Part 3

this should explain it all.

example of an Urban Posh Boy - using a poor man's rap and transform it to a well literated piece of art taking the piss out of the lower classes.
by poshpeoplegonebad December 02, 2010