How should one react if someone tries to tell a 'watching me masturbate story'?

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 tell the person that it is inappropriate and that they don't want to hear such stories. For example, you could say 'This is a private matter and I don't want to listen to this.'

One should immediately look away and give the person their privacy. It's an embarrassing situation for both parties, and respecting the person's privacy is the key.

You should firmly tell them that this is not an appropriate topic and you don't want to hear it.

One should firmly stop them and tell them that this is not an appropriate topic. For example, you could say 'This is too private and inappropriate, please don't talk about it.'

Politely tell them that this is not an appropriate topic for conversation.

Tell them firmly that this kind of story is not acceptable to be shared. Explain that it involves inappropriate content and violates others' privacy. For example, 'This story is inappropriate and disrespects the privacy of others, please don't share it.'

No, it is completely inappropriate. Such activities are private and personal, and sharing or witnessing them without consent is a serious violation of privacy and ethics.

Honestly, the first thing is to stay calm. Don't panic and start making excuses right away. Try to be honest about why you were watching it, if possible. For example, if it was just out of curiosity, admit it.

Tell them that this kind of topic violates privacy and ethics. We should uphold good moral values in our conversations.