While talking to my girlfriend I had the urge to just walk out of the apartment.
Are you guys having an argument?
Not at the moment. I just want her to know that I am upset.
I think that's the wrong approach here. You shouldn't just walk out on your partner because you're angry with her. You should tell her why you're angry!
I'm angry with her because she is always late for dinner and she should know that it's rude and unacceptable.
The only way to fix this is to have a discussion with your partner. Just let her know why you are upset and give her a chance to fix it.