I just learned about the Bielefeld conspiracy, a German in-joke about the town of Bielefeld that is supposed not to exist, and proofs of its existence are just fabricated by them.
In Italy we have Molisn’t, a theory about the non-existence of the Molise region. In fact, come to think about it, nobody in this forum is either from Bielefeld or Molise. It can’t be a coincidence.
So, my question to the non-German and non-Italians (so basically three or four people) is: are there similar in-jokes about your country too?