I think the kindest thing you can do in that situation is address him and set a clear boundary showing him his behavior is not okay, while keeping emotions calm and clear.

I get the sense a lot of people think being kind and compassionate means doing nothing and getting walked on when faced with a confrontation. Well I think kindness and compassion shows itself in the emotions that engage in the confrontation, is it fuel to the fire, or de-escalation with boundary setting? If it turns physical that's another story, but with words it's a game of emotion. And the calmer we are, the kinder we can handle things without allowing anyone to walk on us. But of course, that's just my opinion.

Thanks for sharing this!