1 loosen monitor and tilt until the monitor is disconnected, but not visibly
2 unplug the network/phone line from their computer, if there are two slots, reverse them
3 switch the mouse and keyboard
4 if it is a true war you are having with your target, open the computer case, and unplug the modem, and remove most of the ram. This should make opperating their computer a living hell, however, make sure that there is some ram, so that the computer opperates (it will be unbeliveably slow.