Eh, I just watched the video again. Looks like he was pointing the gun at the guy's friend when he went after him. I probably would have done the same thing.

But it is seriously a VERY stupid thing to post this video up. There's a good chance that some random dude who walks around on the street carrying a pistol and likes pulling it out to threaten people with is f'd in the head and will go WAY OVERBOARD in responding to this (possibly hurting or killing more than just the kid that beat him up), and/or has several friends who act the same way that will come after him and his friends as well.

Posting this video on the internet just gives this guy and his friends a chance to get a good look at all of the kids so they can track them down.