I'm going to criticize my girlfriend.
What about her is specifically bothering you?
She is far too vulgar, I'm not sure if I should be with her.
If you feel that your girlfriend is too vulgar then maybe talking to her about it would be the best option. She may just come across this way because of how she was raised or who she hangs around. Her speaking in a vulgar way does not make her a bad person.
Nah, I'll insult her instead. It's easier.
I don't think insulting or criticizing her is the best way to go about letting her know that you think she's vulgar. I think you should talk to her about it politely, so that she understand what you're saying but doesn't feel attacked.