I have this problem, also. I call it "possuming", ha. I don't think it's a terribly uncommon response. Some of us are just not wired for those confrontational situations. I can usually find some relief by writing down what would have been a healthier response, maybe even sending a message/email/letter if appropriate. But it also helps me to remember that most of the time humans lash out, it has very little to do with you. Fharraige is right - sometimes it's a gift to not be too reactive. At the very least it usually prevents the problem from escalating and might make the other person realize they're overreacting.