Slang for showing someone the middle finger.
Originally a taunt created by the English. During wars between the French and the English, the French would cut of the English captives' middle fingers to disable their bowmen. English bowmen would show French soldiers their middle finger to mean, "you didn't get me."
Eventually evolved (in America only) to mean "Up yours," and later switched definitions to "F*** you."
That bastard gave me the finger!