I think I'm not going to let my gf know my password.
Why are you not telling your gf your password?
Because my gf is a goddamn dick, I would never give her my password
It is understandable to keep some things to yourself, like a password. It could lead to problems with your relationship but she should understand not sharing everything can sometimes be okay.
Uh uh uh, I don't care. I won't share my password and she can shove it up her ass.
I don't think there's any reason to be mean about it, but yes I think it's perfectly fine to hide your passwords from everyone.