Do you know that when fat people order at my McDonalds, I only offer them the large meals?
Seriously? Why would you do that to fat people?
I don't want them to complain that they got too little food.
You are in a place of authority and are abusing your power, that is disgusting. You should treat all customers equally and not based on how fat they are. That is discriminatory and you can get seriously reprimanded for it.
People should not eat too much.
People shouldn't eat too much, and you shouldn't be encouraging them to by only giving obese people large meals either. Let them decide how much food they want instead of abusing your authority like that.