It sounds as if he needs professional help. It also makes a difference if you know the people he is detracting, and does he know he is detracting? Are you taking any pleasure in hearing the next juicy bit of news? If someone continually detracts a person I know, I just tell them outright to refrain from telling me things I need not know because when I see that person, I’m put in a very awkward position knowing, for example, his private sins! If it’s someone I don’t know and 99.9% will never meet him, I can listen to a point, but if it’s a matter on which I can give no advice, then refer him to someone who can help. Assure him we’re still friends, but sometimes friends can’t personally be of assistance. If my friend is attacked by an enemy who breaks his leg, he can moan and groan about the pain, curse out the enemy who did it, but I’m not an EMT, a nurse, or a doctor. The best I can do is call 911 for the ambulance or take him myself to the emergency room.