Let me preface this by saying that I believe that everyone has a different ideal body shape and mass, and that I don't really care about that. However, as a purely intellectual exercise, I have written a fat joke:
_________ is so fat, the DMV made him get turning signals and brake lights installed on his pants.
In fact, I originally came up with the idea when people around me all seemed to be confused about the basics of pedestrian traffic. I thought, everyone should have turn signals, and then I realized that such a requirement fit perfectly into the criteria laid out by the North American Fat Jokes Standards Regulating Body (NAFJSRB), and so why fight it? It had to be a fat joke.