Open Control Panel and double click on Regional and Language Options.

Next, under the Formats tab click on the “Customize this format” button.

Now under the Time tab, enter in the character and / or symbols you think would get a great laugh in the AM / PM fields.  You can basically enter in whatever you want up to 12 characters.   Click OK twice to get out of Regional and Language Options.

Here are a few examples of what you can achieve.  From your name to old chat emoticons.

  

If your co-worker is not aware of this trick … they will have a heck of a time trying to correct it.  Each different example you create will show up now in the drop boxes.    

 

This trick also works in XP.  Control Panel Regional and Language Settings Customize Time tab.

Have Fun!  Please share any funny stories you might have with this one!