I guess I am irrational as I have done it before. Not in a car, but on a bar stool.
Just curious - were you drunk at the time? It's possible that alcohol impaired your normal fight/flight instincts. The normal instint would be spring off of the bar stool before grabbing the person (or, if you were in a movie, finding the nearest pool cue/beer bottle and breaking it in half).
It's all theoretical at this point now that we video evidence just 10 minutes before the confrontation of Brown being a thug. That makes this a pretty easy call who started the fight. Still doesn't justify the shooting without more information.