Where to draw the line

As a parent I feel obligated to tell Mizz to take the fork out of his eye. I think my exact words in perfect mommy speak were "We put forks in our mouths not in our eyes". Mizz hears that as a challenge to then see how many times he can stick the fork in his eye. He is thorough and tries it with both his eyes open and closed. Mind you the fork is more like a plastic spork, but still. He of course freaks out when I take the forks away. To keep himself in the game, he humors me by eating a bite every few minutes. And since he has eaten air, milk, and juice for the last two days I, stupidly, keep him in the chair. I know it's naive of me, but I continue to be amazed at how much he knows what is WRONG to do (moving the baker's rack, plucking fur out of the cat ever so gently, throwing cat food, purposely spilling food and water and saying Uh-ohhh!) and how much he enjoys doing it. I on the other hand am bored with it and would much rather spend the time playing with Legos, Aquadoodle, and ball. I still don't know where to draw the line and don't want to crush his rebellious, playful spirit. On the other hand, I don't want a five year that tears around the grocery store menacing innocent bystanders. I am hoping that like the sleep training, I will know what to do and when to do by following my instincts.