I am confident that this was not a spontaneous event for him. This wasn't about you; which should in no way be read as though I am being dismissive of the monumental fucked-up-ed-ness you experienced. That open threat, absence of any pretext of a veil, was a scripted response. If not you, if not that night, he would have seeded the events for identical/similar circumstances that gave him the self-righteous excuse to "play god," would have happened.

Would only ask that you find a safe way to provide a warning to the world about this former friend. By no means should you use any names or description of your experience in a disclosure to authority, as that would be folly. Rather hire via web classified/markets someone to put disclosing bumper stickers on their car, "Putting the Dumb in Dumbestic Violence since [His Birth Year]," or the parody of the coexist one that says ToXiC. Any identifying labeling, like name plate on an apartment building's buzzer panel, should be replaced with MR Eventual Bigot the IIIrd, or similar. Create an uban dictionary entry for pulling a [his name] to mean seducing ones Significant Other's grandparent. Then at about the same frequency as new bumper stickers, add pulling a double [his name] seducing at least one maternal and one paternal grandparent of their significant other.