Install the Blue Screen of Death screen-saver on someone's computer.

 870

3  

Put tape over the optical sensor of someone's mouse.

 901

1  

April doesn't fool Chuck Norris, Chuck Norris fools April.

 894

0  

Change the coffee in the office coffee maker to decaf.

 1511

1  

Put a "Please Use Other Door" sign on the entrance to your office building if it only has one entrance.

 1540

1