This is a simple, fun, and mostly harmless joke that you can play on people on April Fool's Day. It will (hopefully!) drive them crazy as the words that they are typing start to change into strange and bizarre new words and phrases. If you have access to someone's Word program on their computer then you are all set to go with this prank.
Step 1: Step 1
With Microsoft Word open click on Tools -> AutoCorrect Options.
On the AutoCorrect tab type in a word or phrase or name in the "Replace" field, and then put the new word, phrase, or name in the "With" field. In this example I am going to make it so that whenever Bob Anderson types in his name the AutoCorrect feature will give him a new title.
Here is the final result. In the upper part of the picture Bob Anderson's name appears fine while he is typing it, but as soon as it puts anything after the last letter of his last name (be it a space, comma, period, etc.), Bob Anderson suddenly becomes Bob "King of the Office" Anderson.
You can do quite a bit with this little prank, just remember to keep it something very simple and harmless! You could, if you had the time, add in hundreds of words. But, that would be mean and a pain in the butt to fix, especially if you get caught and have to change it back yourself!