The problem is that we know that intelligent design (in a general sense) is not false, because we know that humans actually practice it. Which is why I'm asking you for a better definition of what precisely it is that can be "falsified."
But you still can't provide a hypothetical observation that would conclusively show that no intelligent designer ever interfered with the historical development of life on earth. That is, "If I were to observe X, then I would reasonably conclude that life evolved completely without intelligent intervention." Nobody is arguing that intelligent design is impossible. People are arguing that either life evolved without any intervention from an intelligent designer or in my case that the idea of intelligent intervention in life is not scientific.