These kinds of verbal altercations are actually very interesting. Being in them many times myself, you can always see the moment in which you have the potential to say something back, or launch an attack on the person. This may be something you can never take back (such as what you may have said), something so devastating to that particular person it seems evil, or a simple retort which may result in a few days of the cold shoulder. The person, in my experience, chooses which road to go down, every single time.
I've made the mistake once, and never again. Better to say something bad, not evil.