How we change what others think, feel, believe and do
If the other person wants to talk about something and you do not, then you can sometimes shorten the conversation (or even kill it stone dead) by pretending that you know little or nothing about the subject.
This is particularly useful when they are seeking information from you. It is not useful when they feel knowledgeable and want somebody else to listen.
Apologize and say that you know nothing. If they persist and start talking about the subject anyway, you can continue to profess ignorance or use another method.
Sorry, but I know nothing about that.
I'd love to help, but that's not my area of expertize.
Sorry, but I don't understand what you are talking about.
Mmm. You're the expert here -- I can't add anything to what you already know.
When you have nothing to say about a subject, then by definition, the conversation gets shorter -- unless the other person decides to tell you all about it.
Sometimes people will ask you about something where they know the answer and more -- they just want to start a conversation in which they can expound at length and 'be the expert'. In such cases, other methods of closing the conversation may be more appropriate.