Cat issues after bad vet visit. . .?

Try to find a cat behavioralist to work with him. He was terribly traumatized and needs some professional help. I'm very sorry he and your family went through that. He could possibly need anti-anxiety drugs for a while. If your vet isn't experienced with cat behavior problems or doesn't see it as an issue, find one who is/does. For at home, when strangers stop by, try giving him a bit of Rescue Remedy (available at health food stores) or use a Feliway diffuser (pet stores) to help calm his anxiety. Good luck to your kitty.