I can't resist a few:

1. Once you have stolen a dormmate's room keys, the room is yours to
   plunder.  As a variation, steal the dorm keys but reverse the lock
   (so the keyhole faces INTO the room); we had a mechanical engineer
   who got this down to about 20 seconds.  Then loudly announce to the
   victim you own the keys, but "let" them win the race back to their
   room.  PRESTO!  Locked inside their own room (with no keys).  If
   you've fixed the phone to continually ring, they get very pliable
   after about 10 minutes.

2. We connected our secretary's electric typewriter to a variac (can
   vary the line voltage).  At about 40-50 volts (out of the 110)
   the little ball makes three or four jerky attempts before finally
   striking a faint imprint.  Fairly pathetic looking, actually.

3. Reverse the horizontal yoke leads on terminals (so the text comes
   out backwards from right to left).  This works best on a software
   team who thinks they have just released the firmware for screen
   drivers.  Besides, hardware people figure it out too quickly.

4. Hand lotion inside of an air hose on the final assembly line is
   effective, but very vindictive.  Use with caution (now, I'm not
   saying I ever did this, but I "saw" it done once :-)

And the standard saran wrap across women's toilets, Karo syrup, flour in
the shower, water-filled surgical tubing jammed in a drawer....ah, for
the good old days!!