A passenger refuses to put a bag under the seat for takeoff. How would you respond?

If a passenger refused to place a bag under the seat for takeoff, I would give a clear instruction and a short reason tied to safety. I would say, "For takeoff, that bag has to be stowed so the area stays clear and secure." I would say it calmly, but I would say it as a requirement, not a suggestion.

If they pushed back, I would avoid arguing about preference or fairness. I would repeat the instruction, offer the approved options, and keep my tone steady. For example, I might say, "I can help you place it under the seat or find an approved storage spot, but it does need to be secured before departure."