Excellent idea: It's always funny to watch an addict freak out over it.
Pouring some sugar on the floor for a coke addict friend of your roommate, after he's been searching the same 2-level 3'X3'X1' shelf for 3 hours straight, relentlessly looking for his lost coke.
That actually happened to a friend of mine in Lake Tahoe in 2007-2008--too bad I don't have the video link cuz it was f***in' funny as hell. He gathered it up, put it in his crack pipe and smoked it, then said it smelled and tasted like cookie dough. Then he asked if he could crash there which they firmly denied and kicked him out.