Okay, so I've seen this question asked before, but literally none of the solutions has ever worked for me, and I've now gone through three phones and six iterations of Android, multiply versions of the Google keyboard, and multiple keyboards and the issue just will not fix. I've seen this common question asked before:
At some point, I mistyped the word "don't" as "Dont" and saved it as an autocorrect. Now everytime I type "don't" it autocorrects to "Dont", with a capital and no apostrophe.
The difference between that question and mine is that I've been trying to fix this for YEARS now. It started on the first version of the Motorola Droid back in 2010 or 2011. Using the stock keyboard, I mispelled "don't" and that mistake would haunt me forever. In 2012 I switched to the Galaxy Nexus. With the stock keyboard, the mistake stuck. I searched for a solution, and only found things like "uninstall keyboard" or "uninstall updates" or "clear cache and data" or "try a new keyboard." The only thing that worked was using a new keyboard, so I used Swype and SwiftKey for most of the Nexus's life. Upon release, I was eligible for an upgrade and rushed to the HTC One M8. The phone was superb... I loved everything about it. Except it's big-keyed keyboard... so I switched to the default Google Keyboard. And guess what was back? My awful "Dont" type. I considered moving to SwiftKey or Swype or any of the other available market keyboards, but the truth is I really like the stock keyboard. I tried reclearing caches, data, clearing out the Search history (like another thread suggested), long-pressing on the word, turning off voice input and long pressing, checked my personal dictionary. The issue persisted. I even side-loaded the beta Android L Google Keyboard, and it immediately reappeared. I totally uninstalled Google Keyboard, Google Voice Input, Google Text to Speech, and used CCleaner and The Cleaner to clear all of my caches and data, and when I reinstalled Google Keyboard, it persisted. I tried the same thing again and re-sideloaded the Android L Google Keyboard... same issue. Froyo, Gingerbread, Honeycomb, Ice Cream Sandwich, Jellybean, and now KitKat and the issue has still persisted. Three different phones, three different manufacturers, three different UIs. The issue still persists.
Please, someone, help. :(
(Why, you may wonder, is it such a big deal? First, it's not fun to answer professional emails from my phone and constantly spell "don't" as "Dont." I'm a teacher, and this looks extremely stupid to parents who expect their kids are learning from the best.)