I think this story is best told in dialogue format. Here's how the conversation between my boss and myself just went:
Me: "Here are the contracts for you to sign."
Boss: "Great. Hey, when are you leaving today?"
Me: (smiling) "Whenever I'm done."
Boss: "When is that?"
Me: "Well, whenever I'm finished with whatever task you're about to give me."
Boss: "Well, when would you be leaving if I didn't give you anything?"
Me: "Uh...probably at 5, so I can finish my homework."
Boss: "Well, then come see me before you go, because I have some stuff for you to do."
Me: "Um, why don't you give it to me now so I can finish it early?"
Boss: "I don't know what it is yet."
All I can figure is that he needs the time between now and then to invent something for me to do, just so I don't get to go home.