My DH does go on about some things sometimes, even to me. I think his time working abroad was very satisfying for him and he looks back on it with pleasure and small comments jog his mind about it. I don't mind because I can say, "yes, you've told me about that several times" but hard to do this when with others as he says that they haven't heard it before.
There are also those who tell the same jokes or funny stories, but they're usually not long so we put up with it - though their partners (typically long-suffering women) are cringing quietly.
I think that if somebody starts on stories about health problems you can stop them by saying that you're very squeamish and you'd rather they didn't tell you. But personally I find health stories interesting, for the first time of telling!
I certainly wouldn't tell a friend that I thought they were boring, there are other ways to stop them.