Is is safe to say how I'm going to swear at a girl who has been swearing at me?
Oh no you don't want to go there, do you? Why would you swear at her?
Because she has been mean to me first
It's reasonable that you want to get back at her. However, it's not nice to swear at anybody.
I'm going to treat this like a game
You can't fight rudeness with more rudeness. Be the bigger person and walk away from it all, and save yourself some added stress. She was wrong to do it first, but overall revenge is never sweet.