A passenger records you on their phone while arguing about a policy they dislike. How would you handle it?

If a passenger was recording me while arguing about a policy, I would keep my attention on the policy and the behavior, not on the camera. I would assume everything I said could be replayed later, so my language would stay short, factual, and professional.

I would say something like, "I understand you disagree, but this is the policy I am required to follow on this flight." Then I would explain the next step once, avoid getting drawn into side arguments about social media or motives, and keep my body language controlled.