My girlfriend's gay friend pisses me off.
What bothers you about her friend?
She makes fun of me that I'm less educated and that I'm bad at cooking.
If you are really uncomfortable with her friend, you tell her so. If she finds it unacceptable that you think you could dictate her social circle, there is obviously some incompatibility issues to work on.
The bitch needs to stop getting in my face.
You can't dictate who your girlfriend associates with, but you can at least inform her of her friend's disrespect towards you.