Should I apologize in person or write a letter

Me and 2 coworkers got in trouble and written up yesterday. We work with a guy who I'll call J. J is missing the top of his front teeth and had behavior that was a bit strange and there was a rumor that he was on drugs. I didn't start it. But I did talk behind his back about it and that was immature of him. Me and people referred to him as Junkie J or toothless J. Yesterday when he was clocking out he went up to me and my coworkers while we were having lunch and said "Just so you know, I have never done drugs in my life. My dad knocked my teeth out when I was 14 so keep my name out of your fucking mouth." Later I got called into my boss's office about the whole thing. I don't HAVE to apologize. I've already been punished but I do want to. If you were in my position would you choose in person or letter?