I had a mischevious roommate in college. Fortunately,

I had a mischevious roommate in college. Fortunately, I was the object
of his machinations only once. It didn't take long to track down my furniture
>from the ten places on campus where he had distributed it over spring break.

His masterpiece, however, was a concerted effort that involved everyone
on my hallway. The victim: our "sponsor" (at Pomona College, an upper-
classperson in charge of a gaggle of fledgling freshpeople).

This one takes some preparation. Wrap very thin filament wire (high
resistance, low flash point) around the fuse of an M80 firecracker. Imbed
this assembly in a box of cornflakes, leading the wires out of the box.

Next, wire several old-fashioned camera flashbulbs in parallel, and put
them in a circuit with the firecracker wire and a 12 V lantern battery. Rig
a solenoid to close the circuit (we used an old clothespin).

Now you're ready. When the victim is out of his/her room, hang the
cornflake box in the middle of the room. Arrange the flashbulbs near the
door. Place the solenoid so that opening the door will close the circuit.
Lounge nearby and watch the fun.

When the victim opens the door, s/he thinks that the room just exploded.
Bright light, loud noise, and the burnt cornflakes feel like a bomb-blast
concussion as they hit your body.

Boy howdy, that woman could run. Caught up with her somewhere around
North Campus. Being dutiful sponsees, we helped clean up the cornflake mess
later.