What I like to do after that moment is ask them why they were so convinced it was a certain way, when it wasn't, and ask them if they either internalize lying naturally as a way of defending the indefensible, or if everyone around them they interact with and every source of information they get is blatantly lying.

I know it's disingenuous, sort of, but I also like when stories get retracted later, because I browbeat them with "That means you were a fucking lying liar for all these months, spewing something that was a total lie. Someone, somewhere, knew it was a lie, and fed it to you because they knew you'd spread their lies for them. All this time, we were right, and you were carrying water for liars, you dishonest vile fork-tongued liar. Why should anything you say ever be believed again?"