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in the middle ages of MacOS (about System 7.5) there was a wee application that lived in the Apple menu called "Shut Down". As the name suggests, it shut down your computer, no questions asked, goodnight Saigon.

First company I worked for full time had a particular member of staff who used to regularly rub me up the wrong way. So one afternoon I nipped in over the office network and copied the "Shut Down" app from her Apple Menu folder into her Startup Items folder. Everything was fine for the rest of the day, but when she came in and switched on her computer the next morning, it ran through the whole startup procedure... then immediately shut down again. And again. And again. And again.

She repeated this a few times, then tech support got involved (another shower of gits) and it graduated to Real Big Fun as the best part of two man days was pissed up against the wall, since of course the computer would restart fine from a CD or with 'shift' held down to disable extensions (and startup items) and had absolutely no hardware or software faults.

Another top Mac knackerer used to be to rename a random file "StartupScreen" and stick it in the system folder. Not only would it spazz out and restart during boot, but it would display an amazing screen full of multi-coloured noise that just screamed "ha ha ha, I am permanently fucked".
(Wong Fei-Hung - now with added flickr.com (see profile), Wed 4 May 2005, 12:57, Reply)