You know, the guy who’s been having that same angry conversation about the same fucking thing he’s been obsessed with for the last 5 years and demands that you take his view while going on long monologues and then immediately interrupting anyone who tries to get a word in edgewise? And then goes into a weeks-long suicidal despair if you try to leave the conversation? Any way to deal with that?
If you engage even one out of ten times, you’re reinforcing it. You can redirect the conversation. Talk to another person, change the subject, completely disengage with them on that specific topic.
You can set expectations privately going in. Set the boundaries. Reiterate them gently but firmly in a general manner. Polite and businesslike when the forbidden topic comes up, cheerful and interested when any other topic comes up. Again, never directly engaging with the forbidden topic.
All this assumes you still want to get along with this person.