To take your silly example, if a source has told me that you've never been to Mexico, why on Earth would your response ever be "show me some evidence" and not "Yes I have"? Unless you hadn't, but doubted my ability to prove the claim. The former response drips with dishonesty and of a person with something hide.
Asking for evidence of points that are not being contended is never rational.
Even *if* my source is mistaken, that is in no way equivalent to telling lies, as you try to misrepresent it. To the best of my knowledge, you are unemployed, *and you have not denied that*, so I will continue to argue that it is true to the best of my knowledge. That you refuse to assert the contrary just gives me further confidence in my source's information, because it is exactly what you would do if you didnt want to be forced into a lie yourself.
Its not for me to provide evidence but you... as you are the one making the allegation.
Have you missed the point or is this a deliberate straw man? I have never asked you to evidence anything. I've just asked for an opposing point of view - something that's always needed before evidence is required either way.