And as a warning to your approach: don't take on the job to make dysfunctional people function for free. Either communicate that you are taking on a burden, or escalate to those whose job it is.
In one instance (literally this morning) "You have to be more specific" was exactly my approach and immediately got to the core issue. In this case there was nothing to be done about it. Our differences are irreconcilable and he's not my responsibility.
In that case trying to understand his deeper motivation was still helpful. It allowed me to have empathy and us to part amicably instead of getting into a shouting match. I consider that the best possible outcome.