I'm going to get angry at my gf and hang up on her
Do you regularly get angry like this?
I don't think this has to do with getting angry or not
It is very rude to hang up on people during a phone conversation, and disrespectful to your girlfriend.  If you are often getting angry with her, you should try to talk about what is bothering you.
I find myself getting angry a lot now.
You should see if you can get help about your anger. It isn't healthy to be that angry.