I'm going to call my brothers girlfriend miss piggy for eating our food after we told her not to
I hope that's not really true. Why does her eating your food bother you so much?
Because she is always trying to do things her way, I hate it.
Calling people degrading names is very disrespectful and reflects bad on you.  If you explain to your brothers girlfriend why you don't want her eating your food, she should apologize and stop doing it.  If you call her a bad name, only drama will come out of it and your brother will be mad at you.
Hmm, I don't care, it's not like she will try and be friends with me anyways!
Don't you want your whole family to have a great relationship? What if your brother decides to marry her, she might not feel very welcome with her in-laws if you keep calling her names. I believe you all should talk out your problems so they get cleared up.