possibly humourous ?

take a floppy disk and drip lighter fuel onto the magnetic inner making sure you get a good coat then take the head of a match that will strike on anything (the red ones) and place it carefully under the metal slide and slide it back to normal very carefully ! When this disk is placed in drive the slide comes back lighting the match and melting the disk inside the drive ! Smoke everywhere.
The old ones are the best, this does work but u got to get it just right and of course remember it will ruin the drive and possibly the whole machine !

(use only in a severe revenge seeking state)

Also if u want to piss off your boss or just play with your secretary or a friend that uses word alot then go to the tools menu and under autocorrect ask it to replace a commonly typed word such as the with another word or sentence like what is going on and whenever they type the word the what is going on will come up instead 9this is really funny to watch !

turn the brightness controls down on the monitors and watch the techie support guys looking really kool checking the connections etc instead of just checking the brightness etc.

Sellotape on the bottom of the mouse.

just a few kool laughs in the office !!!!!!!!

there are loads of otheres too !!!!1

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DISCLAIMER
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I'm not responsible for your stupidity..
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I like to do this on lanparties with lots of (l/g)amers..

As soon as the subject looks away drip a couple of drops of superglue on the mouse..

Step back and look as he goes on with his game of counterstrike..
lifts his hand and raises the mouse...

Since the mouse usualy has a short cable you have time enough to run away...


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WARNING: do not do this to people with courtless mice.. since they CAN AND WILL run after you !!

One of my (harmless) favorites is to take a screenshot of the desktop and then set that as the backround. Next, hide the toolbar and then wait. Its funny to watch people reboot and try to figure out whats wrong...hehe....however, be prepared for revenge.