I will do a print screen on someones computer at work, then hide the taskbar and turn displey icons off. Even if you reboot your settings are still the same(you can move your mouse but nothing happens when you click on icons/taskbar) so some people go crazy over this ^.^
When I was in the Air Force:
We would run into someones room and flip their TV or computer monitor upside down and turn the volume on everything way high then turn the power off.
I would create a task on someones computer in their room to play some random horrible song at 2:30 in the morning
I would ipsend people messages at work saying "I know what you did last summer" or "Get back to work, they are coming" etc etc
Umm I've done a ton more just can't think of them, heres a pic I found ~
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