One of the worst things, in my opinion, is how modern autocorrect fixes words that I’ve misspelled into correctly spelled but inappropriate words. What’s worse is the way Mac OS X arrogantly assumes that I must mean the word that makes no sense in context, because it is closest to the typo I just made.
For me, it’s far better to just see the red line of doom; that way< i can right click and choose the right word, or just type it again. I mean, it's typing; it shouldn't be that big a deal to do it twice. If you're like me and want to turn this "feature" off, here's how.
Launch System Preferences from either the Apple menu, the Dock, or any other app launching system you might have, like Alfred. Once launched, click on the Language & Text icon (it looks like a little UN Flag). Once in the preference pane, click on the Text tab at the top. You’ll see a few options, including the Correct Spelling Automatically one. Ugh.
Uncheck that checkbox, and you’ll still get the benefit of spell check (unless you’ve turned that off, too, you edgy Mac user), but will now be able to make your own decisions about what you actually meant to type. Bravo!
Via: OS X Daily