I'm going to order food just for myself
Why are you ordering food just for yourself?
I hate the way other people eat.
You do not need to order food for others when you are hungry. It is polite though to ask others if they would like to order food also.
I don't care and I want sweets, they're not healthy anyways.
When you ask someone if they might like to order food also, it shows that you are considerate. This is a good way to ensure that people show you that same respect and consideration in the future.