Or dentists, lawyers, old people, Aggies, and especially people who slip and fall.
Because we shouldn't say jokes about anybody about anything, especially if someone else on the planet may have made the same joke-worthy choices or had the same mishap occur.
I've dealt with obesity personally and in my family. My father died at 55 with congestive heart failure brought on by a lifetime of overeating and a sedentary lifestyle. I know how hard it is to lose weight, and obesity is different than being crippled or having cancer or mental retardation. I'll be damned if I'll go oohh-ahh because someone is carrying extra weight and it makes them tired.
Obese people suffer from a set of consequences brought on by their condition - physical, mental and social. That's why it is unhealthy.
You have no authority or experience that gives you the right to lecture me about what I can or cannot use for humor.