You will almost certainly have to negotiate with some people who have pathological personalities. You need to figure out a way to deal with the mental cases you have to negotiate with. Medicating the other person is not an option, so what can you do?
There are three important things to keep in mind when it comes to dealing with difficult people at the negotiation table:
Replace “D” (dispositional) statements with “B” (behavioral) statements.
Label your feelings, not people.
Change your behaviors, ...