So my ex-gf new bf called me and was talking smack?

It was sunday night about 9pm. He called me on her phone saying he was "from the south" and he'll "beat my azz" so I had him meet me at this local park. I'm 21 and he looked 25.He threw a punch and it landed on my shoulder so I head him in the jaw and right hooked up in the jaw followed by an upper cut. He was gushing blood and a few hours my ex called and said I split his jaw bone and he's missing in bottom 3 front teeth, and he was sorry for talking crap. My cousin is a MMA fighter so I train with him sometimes. The problem is I was with this girl I just meet like Friday and she came with me and she sent me a text saying that I'm "a brawler, and if guys look at me your going to knock them out" What are some ways I can show her that I'm really not like that?