Take an old set of bagpipes. Insert and seal in additional drone reeds until you have a set of 5-7 orthoganal reeds (think the f orbital of an atom), with one un-occupied side.
Fill the bagpipes with baby powder or some other non-reactive but pleasant-smelling powder.
Open the prankee's office
using that master key you were supposed to give back to your department secretary but somehow keep forgetting to. It helps if the victim is overly-trusting and doesn't lock his or her office.
Place the bagpipes on the ground, and pull the door closed. Use the handy pull-string (you DID attach the handy pull-string, didn't you?) to pull the bagpipes snug against the door.
When your proposed victim strides purposefully into his/her office, and swings the door open, not only will the contents of the office be evenly-coated by baby powder, the entire office will also be treated to the dulcet sounds of a dozen zebras being tortured.
(for victims with outward-opening doors, an automotive airbag nitrogen generator could be tied to the base of the door, or to a tripwire at the base of the door)