You hand over all of your candy. Marc and his friends fill their knapsacks with it. Marc pulls out some candy and starts eating. "Well, I think that's enough for this year. Let's go home and play video games."
Nicole steps in his path. "I thought you were going to protect us from the Halloween killer!"
Marc laughs at her. "There is no Halloween killer. I just made it up so you'd give us your candy."
They leave the three of you behind. Now you have no candy, and no pillowcases to collect candy in. Halloween is over.
All that's left to do is play a prank on Marc and his friends. Or maybe you should just go home.