lightbrite,
Furthermore, someone who is that angry/deranged/skewed generally is not going to consider what I am saying or any logic for the matter. Instead the person will get defensive.
Yes, exactly. If someone is so outside the bounds of normal human decency that s/he would hurl abuse at someone, or say horrible things about someone to others as if that’s a normal thing to do, then there’s no way that person is safe to interact with.
In my mind, social disengagement is the most powerful response. Stony silence after “jokes” sends a pretty clear and strong message to most people that they have stepped outside of proper societal bounds. What seems more problematic in your case to me was that the store employees were “playing along” with the deranged customer. Rather than being treated like the loon he was, his destructive behavior was reinforced. Given that, the best response would probably still be coldness and silence towards the offending employees, but lodging a complaint with management might be appropriate too. The store managers should know if a customer had a bad experience in the store.