"Ok" is not a word.
When you are writing prose, please take the extra three milliseconds to write the full word, okay?
I don't think the shortened version, OK, is ever necessary, but certainly not in general prose or in dialogue. Sometimes you will see it on signs or written on notes, but not in general use. Please stop it before you give me an aneurism.
(OK can also be confused with the two-letter abbreviation for Oklahoma).
</rant>
OK may not be a word, but okay is not a real word either, it is simply an attempt to make the original OK an actual word. OK was an abbreviation/acronym that originated in 1839 from a humorous Boston Morning Post article that got picked up and popularized by the Martin Van Buren presidential campaign because the abbreviation (originally Oll Korrect) coincided with Van Buren's nickname 'Old Kinderhook'. Then telegraphers (a new invention at the time) began using it as a regular telegraphy shortcut, and OK became part of the English language. It was only later that it was deemed necessary to turn it into an actual word, spelled out, but that is an artificial construct. OK is the actual original term.
Thanks for the input. I didn't do any research, I just know it bugs me.
I will add, my main annoyance is when people write "Ok" or "ok", rather than the capitalised version. However, as people are using the word neither as an abbreviated nor acronymised (pretty sure I made that word up) form of anything (even if it does have obscure origins), there's no need to write it like that—just write the full word! If nothing else, it's more aesthetically pleasing.
I think at one point in my Lush writing career I used to use "ok". Not knowing any better, but I want to say a mod finally approved one of my stories and said "Stop with the ok, it's okay." I wish now I had kept the pm, just to see who it was. For all I know it was Callum. But, it worked. I've used it since and now can't stand when people say ok in any form. It is, in my opinion always okay.
I'm reading Dark Places by Gillian Flynn and I noticed she uses "OK".