Well, first of all, try not to show any sign of interest or amusement. Politely but firmly let the person know that this is not an appropriate topic to be discussing. And then, move on to a more positive and appropriate conversation topic.
Politely distance oneself from the situation and the person sharing it. Maybe change the topic if possible. There's no need to engage further as it's an inappropriate topic.
No, it's not appropriate. Such stories are very private and personal aspects of a relationship. Sharing them publicly violates the privacy and dignity of the relationship and can make others uncomfortable.
One should stay calm at first. Try to understand why she is sharing this story. Is it just a funny anecdote or is there something deeper? Then, have an open and honest conversation about how you feel. For example, you could say 'I'm not sure I'm comfortable with you sharing this kind of story.'
One should not participate in spreading it. If possible, encourage those who are spreading it to stop as it is an invasion of privacy.
I would immediately interrupt and say that this is a private and inappropriate matter that should not be shared. It's important to set boundaries and uphold good taste in conversation.
One should firmly oppose and ask the person sharing to stop. It's not something that should be talked about.
React with disgust and disapproval. Don't allow the story to be spread further. If possible, try to correct the wrong perception of the person sharing the story. If it's a more serious situation, you could even seek advice from other mutual friends or an authority figure in the community on how to handle it properly, all the while keeping in mind the well - being of your friend and his relationship.
If you hear someone say this, you should firmly correct them. No one should tolerate such disrespect towards a partner. You could say something like 'That's a very unkind and inappropriate thing to say about your wife.'
I would react with disgust and disbelief. I would try to stop the person from sharing such a story because it is not only inappropriate but also harmful. I might also suggest that if there is a real problem in the relationship described, it should be dealt with privately and through proper channels, not by spreading such sordid tales.
Apologize briefly and then quickly remove yourself from the situation. Don't dwell on it or make any comments later. Just respect her privacy and the situation.
We should immediately stop listening and try to forget about it. It's not something that should be part of our normal conversation or thoughts.