There is a lovely scene in the animated movie ‘Shrek The Third’ where Pinocchio is attempting not to lie. It goes like this…
Prince Charming: You. You can’t lie, so tell me puppet, where is Shrek?
Pinocchio: Uh, hmm, well, uh, I don’t know where he’s not.
Prince Charming: You’re telling me, you don’t know where Shrek is?
Pinocchio: It wouldn’t be inaccurate to assume that I couldn’t exactly not say that it is or isn’t almost partially incorrect.
Prince Charming: So, you do know where he is?
Pinocchio: On the contrary, I’m possibly more or less not definitely rejecting the idea that in no way with any amount of uncertainty that I undeniably do or do not know where he shouldn’t probably be, if that indeed wasn’t where he isn’t. Even if he wasn’t at where I knew he was that’d mean I really have to know where he wasn’t.
Just like something that is ‘not not difficult’ being difficult, it’s challenging to follow the flow of negation throughout the scene above – and to a large extent, this confusion makes it funny.