OK, O.K., okay
The Associated Press Style Guide prefers OK. They are wrong. I have tremendous respect for the AP Style Guide, but they're eating the Fruit Loops on this one, boy. O.K. is an abbreviation of the folk phonetic spelling "oll korrect" (standing in for 'all correct'). (Quick aside: That phonetic spelling was a Bostonism. I guess we can forgive them. This was in the 1840s and they didn't have the Red Sawks to root for yet. So if AP is going to approve of the abbreviation, it should be O.K. (with periods) and not OK.) I still hate O.K. and stick to 'okay' exclusively. Why? O.K. sticks out too much. It looks terrible. When reading, I accidentally put added emphasis on it because of the goddamn capital letters. 'Okay' has been around long enough to be its own word. The abbreviation is outdated and stupid. The word is 'okay.' Okay?