I'm going to threaten to breakup with my girlfriend of 4 years because she will not tell her parents about me
Is she still in the closet?
It feels like she's ashamed of me.
If she proud to be with you, then she should be fine introducing you to her family. Not doing so for so long does raise questions.
She's acting like a little bitch and I'm going to break up with her if we don't meet her parents.
I don't think it is fair to you or her if she is still in the closet. You both deserve to be in a mutual relationship on the same level. Have you asked her if there might be another problem with her parents?