Maintain a positive attitude when being asked questions focusing on a negative situation or in this case, unpleasant, difficult or combative people. It's being asked for a reason and that is because it's an important part of the marriage or family therapist job you're interviewing for. It comes with the territory so to speak. So give the interviewer an example of how you've handled these types of things before. Avoid dwelling on the negativity and don't vent or relive anything. Instead put a positive spin on your response and address how you've been able to adapt to the various personalities you've encountered as well as overcome or diffuse the situations they create. Discuss how you've learned and grown from every kind of interaction, not just the pleasant ones. It's important for the interviewer to know that you'll fit in without a lot of hand-holding.