cancer... STDs... global warming... has anyone noticed that these are extremely boring ways for the world to end?
i say that one day, ninjas will all develop obsessive-compulsive disorder, and will not be able to stop once they have killed one person. In an effort to fight back, the dictators of the world will join their countries together into one big anti-ninja superstate, and launches a lethal war on the ninjas until evry last one is dead.

<<< an obsessive-compulsive ninja.
america, now threatened by this new superpower, starts to fire nukes at evry country that looks at them the wrong way. a massive nuclear strike ensues, with masses of land becoming uninhabitable. it is only chuck norris, with the help of his 3 bitches (batman, superman and spiderman) who can save the day.

<<<chuck norris about to save the day.
however, chuck norris develops leg cramp. but it doesn't matter, because the day is saved! or so it would seem...
until alien zombies land and destroy every last human before the world is hit with an anti-zombie death star!!! HAHAHAHA! 
<<< an alien zombie.
any questions?