The flying arm bar is one of those submissions that happens so quickly, that you need to look twice to realize what happened. Skip to the 1:10 mark in this video and you'll see Oliver Fontaine pull it off at the Lyon Fighting Championship in France. And you have to feel for his opponent, Sofian Benchohra, who never saw the arm bar coming. With a record of 4-7-1, he hasn't won a fight since October of 2010.
Thanks, MMA Fighting.