Did you ever grow up with "Opposite Day"? It usually happened at school – someone would do something normally out of character or say something obviously wrong, and then exclaim "It's Opposite Day!". This would then create a flurry of conversation where everyone would say or do as many opposite things as possible.
Well, I just realized something. You can't truthfully say "It's Opposite Day" on Opposite Day. If it is Opposite Day, the correct statement would be "It's not Opposite Day", because you're trying to say the opposite thing, but if it's not Opposite Day, the correct statement would ALSO be "It's not Opposite Day", because of course it's not actually that day, and why would you say that? This creates an obvious problem in trying to communicate whether it actually is or isn't Opposite Day, one which can only be solved by proclaiming a future day to be Opposite Day: "It's going to be Opposite Day tomorrow!", for instance. Either that, or when it actually is Opposite Day, you create some kind of code phrase so that everyone...
You know, these kinds of thoughts probably go a long way toward explaining why I was a loner in school...