I'm sure some other people are awful and have done this before, but in Microsoft Word there's an option where if you constantly mispell a word, you can set it so that every time you spell the word incorrectly, the computer will automatically change it to the spelling you've specified.
Of course, this works with things that aren't misspelled as well. If you tell the computer to replace every instance of the word "the" with the entire Gettysburg Address, it will do that, provided you are willing to sit there and type out the entire Gettysburg address. (I am more than willing to do this. I would sell my fallopean tubes, if I thought I could make a good practical joke out of it.)
And this feature isn't good for much other than practical spelling purposes, unless of course other people don't know about it, in which case it is a WONDERFUL way to confuse non computer savvy friends. In college I had a friend who I will call "Matt Rudman," who was from a town called Waltham who I called, "Matt Rudman of Waltham" because we had a lot of Matts and this was how I remembered him.
So while sitting in his dorm room, supposedly "bumming around online" I managed to change it so that every time he wrote out the word "Matt" it would write out "Matt Rudman of Waltham," so that later that night as he sat down to write his paper he called me over into his room to find out, in his words, "HOW THE HELL IT KNOWS WHERE I'M FROM."
Had he waited a bit longer, he would have found that typing the word "and" would have produced the phrase, "and when you finally figure out what I did to your computer, you're going to kill me, but it was worth it to see the look on your face when you typed "Matt" into the computer fifteen times in a row."