I have a big desire to insult my girlfriend's parents
What's the point of insulting the parents of someone you love?
I want to cause them trouble even if it's only a little, don't you agree that they deserve that?
It's never good to insult someone. It's even less good if it's your partner's parents. She will probably get mad at you.
What did I do to make her so upset?
She would be very upset because they are her parents and she loves them very much. Insulting them would be the same as insulting her, and being respectful to everyone in a relationship should be a given. Please reconsider this, wouldn't you rather foster your relationship so everyone is happy?