Not sure where it came from, but of course everything is blamed on Vietnam or earlier military events, like Roger Wilco and FUBAR, but I do know "OK" is uniquely American in how it is said and uttered. For example, I've had German relatives try to say the word and use it and they sound facetious or insulting because they use the wrong intonation. It's a bit like an American trying to learn and speak Chinese. A whole lot in how a word sounds is missed and can be misinterpreted when you're not part of the home culture.
Not sure where it came from, but of course everything is blamed on Vietnam or earlier military events, like Roger Wilco and FUBAR, but I do know "OK" is uniquely American in how it is said and uttered. For example, I've had German relatives try to say the word and use it and they sound facetious or insulting because they use the wrong intonation. It's a bit like an American trying to learn and speak Chinese. A whole lot in how a word sounds is missed and can be misinterpreted when you're not part of the home culture.