To prank your coworkers is an art form - and should not be taken lightly. You need to have the right tools at your disposal. For instance: a mannequin that can be placed throughout the office to scare unsuspecting coworkers.
Feel free to dress it up (or dress it down) to suit your needs. However, if you are the prankster at the office, keep in mind that a scheme from the other coworkers just might be in the works.
The moral of the story is... prank your coworkers and have fun, but remember repercussions are merely a Nerf gun fight away.