These mammals are extremely overprotective of their "Diet" food. If approached while they are consuming, the obese creature will attack with cow-like reflexes. When told to go on a diet, they will tend to bitch and moan about how they lost 3 pounds over the past 5 months.
Skinny person: Frank you really need to go on a diet.
Frank: Suck my dick!
Skinny person: Whens the last time YOU saw your dick?
Frank: ...You jerk! *cries and eats bucket of ice cream*
Skinny person: I hate fat people.