I came across this spoof documentary or mockumentary about London from the Londonist blog. Essentially, it tells you everything you ever wanted to know about London's history, if you don't care about things like facts or accuracy. As a spoof it works fairly well and is certainly worth a watch.
Some highlights include the secret order of the black cab which controls London, the fact that the Thames was a gift from Egypt and that the rich don't bother with regular Oyster cards, but instead have their own special payment system. There are plenty of other amusing bits as well, that will get you sounding like a true Londoner in no time.
While not the fumiest thing I've ever seen, it will make you chuckle, especially if you know a thing or two about London's history and landmarks.