A violent act in which a person is made to bite the edge of a sidwalk and someone else stomps the back of their head. This generally causes massive head trauma and results in the loss of many of the front teeth. The term originated in the Kensington neighborhood of Philadelphia, a notorious Irish slum, incidentally an area where oral hygiene is quite poor, possibly as a result of the Kenzo Mouthwash.
That pussy from American History X stole the Kenzo Mouthwash from us. Now suburban kids who want to pretend they're hard talk about dishing out curbies, but all they don't have curbs in expensive neighborhoods!