OK... - "This is exasperating and I'll just accept it"
OK... - "His response was childish; moving on..."
OK? - "What you've just said appears to have no bearing on the question I asked nor the conversation at hand. Please explain how it's relevant or get on-topic."
OK? - "Did you understand? Please provide a response indicating whether you need additional information."
OK! - "I acknowledge your request and am capable and willing to fulfill it. I'm on it. I'll get it done. You can count on me."
In person, you can provide vocal inflection and facial expression to communicate which of these you intend. Over text, you're at the mercy of how the reader is feeling in the moment. Personally, I'll spend time either putting more punctuation around the "OK" to help clarify. Or I'll just go with the sentences that attempt to preclude ambiguity. Apparently (anecdotally), most people don't bother.
OK = Acknowledged or agreed.
OK? = Request for acknowledgement or agreement.
Anything else is reading too much into it. If I send someone an email explaining something and I get an, "OK" back, then I assume they've read it (or will read it) and I'll hear more from them if they have more to share.
When speaking in person, the "OK" itself almost completely superfluous as it's merely a vehicle for inflection and other social cues which carry the real meaning, as you noted.
> I'll just go with the sentences that attempt to preclude ambiguity.
And that's what I'd do 99% of the time, but I was specifically pointing to discussion around "OK"
OK... - "This is exasperating and I'll just accept it"
OK... - "His response was childish; moving on..."
OK? - "What you've just said appears to have no bearing on the question I asked nor the conversation at hand. Please explain how it's relevant or get on-topic."
OK? - "Did you understand? Please provide a response indicating whether you need additional information."
OK! - "I acknowledge your request and am capable and willing to fulfill it. I'm on it. I'll get it done. You can count on me."
In person, you can provide vocal inflection and facial expression to communicate which of these you intend. Over text, you're at the mercy of how the reader is feeling in the moment. Personally, I'll spend time either putting more punctuation around the "OK" to help clarify. Or I'll just go with the sentences that attempt to preclude ambiguity. Apparently (anecdotally), most people don't bother.
OK?