Don't let your significant other define you in ways you don't yourself want to be defined. If this girlfriend of yours truly cares about you, then she would not want to bring you down a path you are uncomfortable going. Granted, don't assume she doesn't care. You may have unintentionally made it sounds like you wouldn't mind getting piercings. Tell her frankly that you don't want any and if she insists you get them regardless, take appropriate action.