How offensive you may ask? It is often compared to the offensive gesture known as the middle finger. The action of this insult is commonly performed by flicking the V upwards from wrist or elbow.
The origins are wrongly attributed to a story of an apparent gesture made by English and Welsh longbowmen fighting during the Hundred Years’ War (1415). According to the story, the French were in the habit of cutting off the arrow-shooting fingers of captured longbowmen, and the gesture was a sign of defiance on the part of the bowmen, showing the enemy that they still had their fingers. However, there is no evidence of French forces cutting off the fingers of captive bowmen.
The real origin will most likely remain a mystery because of the taboo nature of the sign. “It has been passed on from generation to generation by people who simply accept it as a recognised obscenity without bothering to analyse it.” —Desmond Morris.