Does anyone else dislike the use of "I'm good" when declining an offer of something? As in:
"Would you like some more coffee?"
"I'm good."
I don't understand why people think that "I'm good" is a polite substitute for "No, thank you" or "No, thanks." Sometimes it even sounds less like a gracious decline than a curt rebuff.
(I resist the temptation to say, "I'm glad to hear it. And would you like more coffee?")
I get that it communicates that they don't want the coffee. But it does not communicate any acknowledgment that the person offered them something, just an announcement of their own satisfaction, coffee-wise.

Okay, that's obviously not the problem! What's actually wrong is that they aren't expressing any gratitude for the offer. Which is what polite people do when either accepting or declining something.
It was so easy to teach our kids this. We just treated it like that was the words you use from the time they were tiny. "Thusnelda, would you like an apple? Yesplease or nothankyou?"
In my opinion, "I'm good" is just as rude as plain "No."
"I'm good, thanks" is okay.I wonder how omitting the thanks got started, and
why people who would never just say "no" without "thanks" think "I'm good" without "thanks" is okay?(ETA bolding to clarify the point of the objection.)