If your freind seriously tell you that, you also will be supposed to answer them seriouly. But there is another case. for example, your freind just wants to talk about anything with anyone.
In Japan of particular west range, some people called "kansaijin" often use an evil words in such a scene. That is "shirankedo". It means that I don't know.
They very often use the words. They can use it at a saying of both beginning and end. If they use it at the beginning, we are not annoied. Because we can understand their feelings to our talking.
However if they use it at the end, It does bother us very much. We can't see that with what feelings they listen to our saying. I will feel so bad, if they use it after we seriously finish to talk about our future job to them. So I will also try not to say it, shirankedo.
