Gank
Noun - Gank (Archaic Flemmish): A firm hit to the crown of one's head with a closed fist.

Verb - To gank: The act of hitting the crown of one's head with a closed fist.
A posse of chavs confronted me, whilst tending to the evacuation of my bladder in an intimate alley behind Oxford Street, and spewed forth a particularly degenerate form of vernacular; henceforth, I was compelled to offer them each a swift gank to their craniums in order to assert my disapproval.