So why didn't Michelangelo paint The Last Supper?

There's very little argument to the proposition that Michelangelo was the greatest Renaissance artist of all time (and not much argument that he was the greatest artist who ever lived, period).  Not only did he set the standard for sculpture (Pieta, David, etc), but he painted the Sistine Chapel ceiling.

So how come he didn't get the job to paint The Last Supper, which is Leonardo Da Vinci's most famous painting (along with the Mona Lisa)?  Monty Python explains it all for you.