I'm having big problems with my boyfriends EX girlfriend, HELP?

Ok so im a girly girl and my boyfriends ex is really ruff, tatoos into rock and fights alot. I was out last night round the town with my girl as it was my best friends 21st. She always wants to fight me and asks me to take it outside, i dont even do anything wrong. Ok so i do have an attitude problem only because im sick of her been so childish. She is nearly 30 for christ sake. What can i do about this situation.