Conversation:

I'm an American, so the first time I ever saw the two-fingered 'rude gesture' was while attending a performance of Shakespeare's Henry V. When Mountjoy the herald exited with his escort after talking to Henry, all the English soldiers faced Mountjoy, did the two-finger thing, and yelled, 'F*** you!'

I wonder now if this was inspired by the theory that the gesture arose at around the time of Agincourt.