Work (harmless) pranks thread

I used to be a big fan of getting to the office early and stealing the ball inside everyones mouse. I worked in a large company and I would have 30 mouse balls (mouse balls, jeez is there a better way to put it). I only did it once every couple months.

There is another thing I did where i would take a screen shot of their pc, put all the icons on there desktop into another folder, and put the screen shot up as the back ground. Now there is no icons to click on, however it looks like there is.