I think that you handled it well.You encountered someone with a short fuse or paranoid.Your virtual lack of response in light of his out in the open dance, helped to defuse it.I've been in somewhat similar situations,ignoring them or a small apologetic wave is best in my opinion.If you had made a different gesture,hit reverse,or zoomed around him, it might have "game on". He vented his steam,but he also knew that longer that he was outside of his car,acting up,the more that he might look an idiot or hothead to other motorists......and who knows..he may had been rear ended in the past,and didn't want that to happen again.He might even have noted in his mirror that you were also distracted with your breakfast,which stepped up his worry.