Sticking two fingers up at somebody, flicking Vs.
A reference to the Norman invasion of England. When the Normans captured Anglo-Saxon archers, they would cut the archer's index and middle fingers off.
So as a act of defiance, unmolested Anglo-Saxon archers would rebelliously stick those two fingers up at the Normans.
He was being really haughty with me, so I said "up yours" and gave him an Anglo-Saxon salute.