Hard drive transplant
Okay Here is an ingenious way you could strike terror to you colleagues.
It a weekend prank that requires hell lot of time to implement.If you know any IT guru nearby , have them remove your victims hard drive and replace it with another. (make sure you have an expert with you , who is able to reverse the procedure after the prank is done)
Of course the general assumption is that nobody ever backs up their data. when the user boots the PC , an error message will be displayed (ofcause you installed a dead hard drive) . Whatch them as they frantically call the help desk assuming that all their data is lost!
Kindly inform them its not.. and replace their original drive… (thats why you need an expert )
have fun take some shorts with you enjoy the moments!