Social workers meet with different kinds of clients. They often struggle in life, face problems and are unsatisfied with everything around them. (That is the reason why they need your help).

Being overwhelmed by their own problems, they can be aggressive, angry, sad, irate, or whatever else comes to your mind. Some clients are nice, but many are not. As a social worker you need to handle all the people and all the problematic situations. That is why you will be inquired how you dealt with such clients in the past.

Notice that it is a behavioral question. Recruiters ask what you did, not what you would do. Therefor you should speak about a situation from the past, ideally from your job. But if it is your first job application, you can calmly talk about experiences from your personal life.