Once a psychologically disturbed patient was taken to a mental hospital. 

The psychiatrist told him to count bugs as a way of confirming treatment, he poured many ants into a transparent container and asked him to count them, numbering in their hundreds to thousands these creatures were really stubborn, highly mobile, when you get down to labeling each one of them others are already crawling out of the jar, it’s the silliest exam in the whole world. Here is how the results are going to play out…

 if he disagrees with the proposal, if he turns down the offer saying it’s a foolish thing to do,  it clearly indicates he could be having a clear mind-set, and only pretending to be mad. But if he blindly accepts that proposal, and enjoys the whole affair, laughing giggling etc. then you certainly know he is out of his mind. All madmen think(believe) everybody else is crazy while they themselves are okay.