Here is one that i mentioned before (probably everybody knows it):
There's three leaders: Fidel Castro, Bush and Bin Laden. Suddenly a genius appears and sais that he will give the three one wish. Then Fidel Castro sais that he wants a fence to surround all Cuba so everybody stands there, and the genius grants it. Bush thinks for a while and then he asks for a great wall that proctects all USA from terrorist, the genius grants it. Then Bin Laden looks at him and laugh, and then he asks the genius "i want you to fill the walls with water". And the genius grants it.

Well yes, it's really dumb i know.