You are describing a kind of insanity (psychosis) that is self-chosen. My own view is that the only way to create a "psychotic break" and shock the person out of their insanity is to confront them with very strong cognitive dissonance. In other words, factual reality in contradiction to their delusional view of the world and themselves. This means you will need to have a very firm grip on the facts of reality. It will be a kind of benevolent gaslighting, where the purpose is to deflect them from their delusion. They will get puzzled at the appearance of two realities, vis-a-vis them and us. They will disconcerted when we blithely point out their hypocrisy and not show that we care one whit about it. (Being disregarded is the first step of personal humiliation. Being a subject of humor is the second step.)

To invoke the famous line, this won't be for everyone. Some psychopaths are naked predators in the shape of human beings, and imprisonment or death for them is the only way we can have peace among ourselves.