Any negativity is an impediment to peace. Can you speak to him to find out what his payoff is in doing this? Maybe he has some issues he needs understanding and compassion with. I would try to speak with him to find out why he needs to do this. If this is just his personality, you may have to distance yourself emotionally from his reflections and tune out his negativity. The other thing you can do is to ask him not to criticize around you as it messes with your chi.