I don't know what I can add - I think the OP handled himself perfectly and that drawing his gun in a ready, but not aimed position is very likely what I would have done......actually have done once before when I couldn't just drive away.
As far as "brandishing" goes, I see it more as the OP was simply making sure he had access to his firearm in case he needed it. He was still in his car and did not threaten the idiot. If he had a permit (at least in my state), he could have had that gun just lying on his front seat - no problem there.
If the idiot blocks you in with his car and his body, proceeds to aggressively strike your vehicle, it's not that easy to just drive away. You may have to make the decision to run him over, hit the guy's car, or damage your own car (and possibly get it stuck) trying to get over a curb/grass to get around. At that point you may genuinely feel trapped and need to get the guy to back off before you can drive away.
Last edited by Skans; April 3, 2013 at 08:16 AM.