I'm mad at someone for not getting me food
Why do you think they should have gotten you food?
Because I told them to get food for me.
It's not right to be mad at someone for not bringing you food, because you can't expect other people to do whatever you say. You should either get food for yourself, or ask them politely to get you food. You shouldn't demand that they do it.
It's so unfair, I can't get what I want. When have you ever heard of anything like this.
Don't act like an entitled brat, get used to the fact that you're not going to get all that you want. There must be a genuine reason for not getting your food so no need to get mad at them.