Two passengers start arguing during boarding. How would you handle it?

If two passengers started arguing during boarding, I would step in early before the tension spreads through the cabin. I would use a calm, firm voice and say something like, "Let us pause for a second. I need each of you to give me space so I can sort this out." Then I would separate the conversation enough to lower the volume and quickly identify whether the issue is a seat assignment, bag space problem, or something else.

I would avoid taking sides or matching either passenger's emotion. My job would be to restore order first and then resolve the actual issue. If the problem was simple, I would give a direct next step and move boarding forward. If one passenger kept escalating, I would involve the lead crew member quickly rather than letting the aisle get blocked while the conflict grows.