You ever been in a fight with your wife and she insults the size of your penis? My GF just did that to me a few days ago and I don't know how to feel about it.
I’m always insulting my own penis. Holly never has. Not even in the midst of heated argument. Maybe she’s saving that for some gigantic fight in the future. That’s in reserve ammo.
If your girlfriend insulted your dick in anger, then I’d explain to her how hurtful it was and tell her not to do it again. If she did it casually, then you might want to consider telling her to hit the road. That’s not cool at all.