Like you, I can become very hurt when people are mean spirited. I'm sorry to hear about your stupid experience.
I have a friend who, when really agitated by a mean customer simply replies with "Now, you are not being very nice."
A long long time ago I experienced something similar to you. On Christmas eve, a recipient of ours came home to find his flowers had been left with a neighbour, and called in a mad fury to say that that was a breach of contract...that we had been contracted to deliver to his residence, not to the neighbour, and we were incompetent, and he could break a leg going to the neighbour's house, and he would take us to court, and we would not last another month once his lawyers got through with us, that we would be sorry etc. etc. etc. Nothing would calm this asshole down, even an offer to go pick up and re-deliver the flowers, on Christmas Eve no less! No matter how much I tried to reason with him, it got worse until I became very upset, and began to tear up.
And then I remembered my friend.
I said to him, really really calmly, "Now, you're not being very nice are you? We have done everything to serve you, to the very best of our abilities. In return, you are being very mean to me. I'm sorry, I will not discuss this with you any further until you calm down, and remember your manners." Then I hung up.
I fretted about it all through Christmas, but sure enough, came back to work to find an apology on the answering machine.
His name and address is posted in the shop. We will not accept an order, or deliver an order to him again.
But, if nothing else, at least he learned that there is one woman who will not be bullied.
Oh, and don't worry about a lawsuit. This is Canada, and it would cost him way to much to even think about it. He's just a jerk.