At first it seems like the op is paranoid and over reacted but it's all about perception and what you feel are your abilities to defend yourself in a situation. If you're a physically big person you might not react the same as a smaller person would to a perceived threat. Maybe you have extensive hand to hand combat skills so size would not necessarily be a factor as opposed to someone who does not posses any defensive hand to hand skills.
I have been in very similar situations; in traffic or otherwise in my vehicle and someone is not paying attention or maybe I wasn't paying attention. I have not reacted the way the op did in his particular case but I'm a big guy with hand to hand skills so I perceive situation differently as do all of us. We all have different threat meters.
The op didn't brandish his weapon. He didn't act like a tough guy because he had a gun. He got out of a confrontation with words.
Why don't you wear your gun in a clip on holster or something? The carry setup in your vehicle is not tactically sound. The gun should be attached to you and not to your vehicle. Having the gun already in your hand, even just to get it out of site, is a potential accident waiting to happen IMHO.