Surely it's just a shortening of "I'm feeling good"

I don't think it is particularly an Americanism and I remember people saying it long long ago.

Much of our language is borrowed so even if it is I see no harm.

The only appropriate response to such a question is to say "Spiffing, dear thing. Absolutely spiffing!" whilst twirling one's moustache* in a cavalier fashion.

*That's 'top lip hair' for those offended by foreign words.

What does 'a thing' mean?

A thing what people do, obvs.

Moustache isnt their worry for purity.

Spiffing, isn't that believed to be a based on an American term for being drunk?

Absolutely derives from Latin. One of them f*cking romantic language words innit.

We'd want "good, dear thing, good"...

Oh... bugger

Maybe but there are over 30 different meanings of 'good' in the Online Oxford Dictionary and even more usage examples! The meaning/usage you don't like is in there.

Good is just a versatile word that can be used for almost anything positive.

Hmmm ... sounds a bit Germanic.

Perhaps a variation such as "Jolly good. What ho!"

Hmmm...

Aside from it sounding like a bad parody of a toff, good is Germanic, and its the OP's trigger word.

Are such peoples issues with Germanic languages though? What is their expectation for our language.

A 'thang' as my mother would have said.

Ah, yes.

In order to avoid saying 'good', perhaps we should settle on "not bad".

That works...

"Are you not bad?"
"I'm not bad thanks!"

Perfect! 😁

I think I've just spotted a problem.

If "I'm not bad, thanks" isn't the true answer, do we say "I'm not not bad", "I'm bad" or "I'm not good"?

I think you all need to get out more.

A lot of the other kids used to say that when I was in primary school (1973-ish). 'I wasn't here last week because I was bad.' Or 'My brother's bad so he won't be in today'. It's not an expression I've heard in years and I just used to think it sounded a bit weird. It's definitely nothing new though.

because it`s polite to answer.

So as you are obviously anti anything American I guess you've never used a McDonald's or KFC, or watch The Simpsons, etc etc.
I really don't understand this stupid attitude. It's a real Victor Meldrew miserable git attitude.

Genuine first world problem. There is absolutely nothing wrong with it. It's as good as "fine thanks or" not too bad really thanks ". What tf do you want them to say?

I don't mind it personally. Certainly less annoying than sayings like 'my bad'.

We gave the world our language (which itself is a mash up of other languages, but let's not over complicate things) so we are bound to find it evolve and come back. It's not just the US, 'no worries' is a common thing to hear now.

Same here. Usually I'll politely answer "I'm good thanks, how are you?" or something generically similar. Plus it's better than the truth sometimes as the honest answer can be -

"No, I'm feeling really bad right now thanks to my depression, to be honest I don't even want to look at you let alone attempt to be pleasant. In fact if you can point me to the nearest rope that would be great"

Obviously I wouldn't do that and that's where "I'm good thanks, how are you?" comes in.

In cases Santa's listening.

Why do people you work with have to ask you how you are every day???

I know but you can't not answer although one of old colleagues did as he was tired of always being asked. The silence was so funny.

I'm fine, thanks for asking.

I used to like Mike Dicken's response on the radio - "my health is not in question"

You could reply 'not too good' thanks. Now that DOES make sense. Saying I'm Good doesn't.