I'm refusing to eat the food that my girlfriend's parents made for me
Why are you refusing to eat the food that your girlfriend's parents made for you?
They used too much oil and salt.
It's rude to refuse eating food your partner's parents cooked fo you. Grin and bear it for now.
Nah, I'll cook for my girlfriend since I care about her.
It is really rude to refuse the food. Unless you have a medical condition you should attempt to eat some of it. If you reject it it is seen as a rejection of them.