Write a message on an upside-down paper cup that alludes to something horrible being trapped under it. Leave it on a coworker's desk or in a conference room.
 1559
1  

Hide all of the desktop icons on someone's computer and replace the monitor's wallpaper with a screen-shot of their desktop.
 967
0  

Change the coffee in the office coffee maker to decaf.
 1528
1  

Find a sleeping person, fill their hand with shaving cream and then tickle their nose.
 846
0  

I just recently discovered that there is a national holiday named after Atheism. April FOOLS day. Like this story in the name of Jesus.
 2065
0