This is surprisingly good advice. Speaking as someone who has literally seen red with rage (it's not just an expression, everything in that moment DID turn red for me), and as someone who has intervened to stop a guy chasing a woman with his pickup truck.
I hate violence. I was in a movie theater with friends, near the ticket kiosks, which were all crowded and a large muscular jerk who was visibly drunk, got agitated trying to buy a ticket, shoved my then-pregnant friend and boyfriend. They were unharmed, but shoving match ensued. Seeing my friend agitated, I brought attention to the situation by yelling loudly "Hey what's going on?" and trying to get other people to witness the shoving. Muscle jerk turned to me and said "oh, you wanna fight too?" I replied "No, I don't fight. If you want someone to fight, I'll call the police." I then started to ask for security from the theater workers who pretended not to notice. Fortunately, muscle jerk's anger had enough time to dissipate, and left.
You will be better able to deal with the possibility of violence if you can stop "hating" it. A way not to hate violence is to understand it. Hating violence is like hating sickness... or extreme youth. Sick people can heal. Young people can grow. Hating about these things will either have no effect or, at worst, delay the improvement process.
Generally, people want to be respected. Show them respect and they are likely to calm down.
Generally, if someone is weirdly upset with you, and you know you did nothing particular to provoke it, then their anger is not ABOUT you, EVEN IF it is directed toward you. Usually, showing empathy and sympathy and respect will have a good effect, here.
Above all, be as patient as you can. The emotionally more stable person must hold his emotions in check while the less stable one goes through his own process.
I have been the angry guy, defused by a patient listener. I have also been the defuser. I once managed to get a psychotic fellow to leave the middle of a street in Manhattan, and got him to yell at me for 20 minutes so that normal traffic could resume. I listened to him (demons were invading NYC and he wanted to warn people). I also once came within a few seconds of using my car as a battering ram in road rage caused indirectly by personally devastating news from the previous day. I was in a fragile state and didn't realize it.
Don't hate violence, as such. Hate the effects of it or the necessity of it. But if you can stay calm in the face of ungovernable emotions of others, you will make the world better for everyone.
This advice works for me, and has worked ON me.