If you're looking for a simple, yet infuriating practical joke, the Filing Cabinet Frustration gag is just what the doctor ordered. I'll also share a neat twist for those with a naughty streak in them.

First, you'll need either an old wind-up alarm clock or an electric one that you can put batteries in.
Next, find a place where your suspect will be for a period of time, like an office or home desk, car glove compartment, etc.
The key to this prank...is the key. Wherever you "plant" the clock, you need to be able to lock it up. Set the alarm to go off when your suspect will be next to it. And sit back and listen to them cuss and groan because they can't shut it off!
Now, for those who like to go the extra mile (and possibly get fired), here's how Yours Truly would pull this prank. Use a cell phone that you can download a ringtone to. Find a tone that mimics lower intestinal bodily noises and make sure to turn the vibrate function off. Then, put it in your boss's briefcase or underneath the conference room chair he/she likes to sit in. At the right moment, have someone repeatedly call the cell number! It wouldn't hurt to find a way to film the look on your boss's face and those of the unsuspecting co-workers or people he/she is meeting with.  Remember, deniability is always a good thing when pulling a prank of this magnitude.  And if you think ahead, you might consider stea....uhhh, borrowing a buddy's phone. They'll feel the wrath and you'll double the gag!