Here the other day while my two colleagues where out, I got an idea for a practical joke. We work with user support and PC repair. Like any good(?) IT personnel all our PCs are permanently open(Well, if we are going to hack the PC every day or so it might as well be open...). Anyway, I took a screen grab on our internet PC and modified it with weird colours and put it up in full screen. Then I took a jumper and put it on the 'keylock' pins on the mother board, thus blocking the keyboard and the mouse. And went to lunch, were I meet the other two.

When we came back, they noticed the strange picture. They tried the mouse and the keyboard. When that didn't help they rebooted, to no use. Next one of them checked the keyboard connectors, finding nothing wrong he pulled it out and put it in again. This was when the other one saw that the lights on the keyboard flashed once, as it was plugged in(The keyboard's microcontroller starting up). He thought this meant the keyboard only worked that second(and then was powered down). So he told the other one to plug it in and out continuously while he pressed the enter as fast as he could...

At this time I just couldn't take any more and started laughing.. So they told me to fix it, if it was so simple... I just pulled the jumper and normality was restored.

Afterwards they too thought it was a good joke.