Put tape over the optical sensor of someone's mouse.
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Hide all of the desktop icons on someone's computer and replace the monitor's wallpaper with a screen-shot of their desktop.
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Place a pair of pants and shoes inside the only toilet stall in a rest room to make it appear someone is using it all day.
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Paint a bar of soap completely with clear nail polish so it won't suds up.
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Remove the shower head and place a chicken bouillon cube in it, then put the head back on.
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Put a "Please Use Other Door" sign on the entrance to your office building if it only has one entrance.
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Find a sleeping person, fill their hand with shaving cream and then tickle their nose.
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Fill someone's hair-dryer with baby powder.
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Take a squirt gun into the rest room stall next to someone and shoot little drops over the wall every couple of seconds while pretending to pee.
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Write a message on an upside-down paper cup that alludes to something horrible being trapped under it.
Leave it on a coworker's desk or in a conference room.
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