Draw from your past experience to describe how you have dealt with a similar instance. The interviewer is getting a sense of how you respond to security threats.

"Before entering into the security field, I worked in customer service jobs. It allowed me to hone my people skills and learn to communicate effectively. In my last position as a retail security officer, a customer got extremely upset. She began yelling and damaging clothing displays. I allowed the woman to explain herself and voice her concerns. Then, I assured her that the matter would be handled, but the best way to get the issue resolved was by remaining calm and discussing the situation with the store manager."