Peasblossom, yes, I know many with a favourite, predictable topic of conversation. I make great efforts to chip in with something different, and ask lots of questions, to change things. I get the impression that it's not really a conversation at all. Rather, they are 'broadcasting' to an audience (any audience).
If I really can't face them, I'll make it clear that I have a meeting/appointment, so can only do a quick chat.
Once, I spotted a neighbour just like that approaching. Unable to face the long chat and delay, I crossed the road and turned a corner to avoid them. Unfortunately, I met, head on, another one!