People who are vengeful and hold grudges and act on their grudges are the worst type. Cut them out of your life as early as possible.. Dangerous to your life...
Do not try to cause drama or react or give them attention. Disassociate and be polite and hope that they will not come back with revenge.
I have never been a vengeful man, in fact, quite the opposite. Someone is testing my goodness. I am not going to freak out. I am going to stay calm and keep on with my good life.
Let him be alone with himself - shitty stupid person that he is in a prison of his own mind.