A couple of years ago I had the job, at a point to point, to try to sell raffle tickets for a well Charity amongst the race goers. Most of those I asked were/appeared to be upper class ***** and the only answer I got was 'I'm good'. I felt like saying 'No you're not, you ****!'. I soon gave up.

Because language changes constantly.

I've never thought about it. Nor did I realise it was (allegedly) an Americanism. People have been saying it for as long as I can remember, and I grew up in the 90s.

If I'm asked, "How are you, or how you doing? I'll reply ,"I'm fine thanks, and you?"
If I'm in a bar, have a nearly full glass, and get asked, "Want a top up, or another drink?" I'll very likely say, "No, I'm good thanks", likewise if I'm in a restaurant and the waiter places my dinner plate on the table and says, "Mustard?, Parmesan?, another bottle of wine?" I'll probably use, "No, I'm good, but thanks" again there.
It's probably something that I've picked up in the U.S., as I'm often there, but it seems to fit.

What about if they say "not too bad thank you", which pre-dates any Americanism influence, by many decades.

the stupid attitude is yours. People are quite capable of using American products or watching American television shows without feeling the need to adopt Americanisms like trashcan, side walk or fawcet....or "I'm good" "Can I get...?" , "Awesome" and "Period"

Any British person using Americanisms because they think it makes them sound 'cool' just comes across as rather sad.

I always say "not bad" which is just a pessimistic version of "I'm good" I couldn't bring myself to ever admit that I am good, that's like saying I am a saint

It's just Valley Girl Talk, taking over the English Speaking World. The triumph of the A.Q.I. . While everyone watches Donald Trump, closely, USA ''reality tv'' is taking over the world ..........

The point of language is to convey a message. As long as the message is understood, that's the main thing.

Presumably the OP has never understood what someone means by "I'm good".

I hope this thread has cleared up the confusion by explaining that the word 'good' means pretty much the same as 'fine' or 'not bad'.

Perhaps the OP might now add it to the "What really obvious thing have you only just realised?" thread.

I like to say "yes strong thanks"

It confuses people

And I reply, "What the ******* hell's it got to do with you you nosey £&#@.

Okay, the emoji tells me that you're kidding, but how about if a good friend or neighbour asks you "how are you?".

One of the meanings of good is well.

I don't understand why anyone says I'm good instead of no thank you.

To be asked how you are these days is refreshing. Large numbers of people seem to be locked in their world of text, ( I watched a young texting boy walk into a bus last week.)
Good seems good to me, no worse than cool or the absurd OK.

The best thing when people ask how you are is to reply 'as well as can be expected under the circumstances' and then walk off sharpish.

The OP knows what 'I'm Good' means. It's just that it doesn't make sense. It's like saying "Hi how are you" "Yes I'm well behaved thanks".

You don't hear people saying to kids "I hope you've been a fine boy or Santa won't bring any presents".

And that's it in a nutshell. That's why people say it.

There's one guy at work who always says "Not three bad thank you"

Another one always says "Ace, my son, you?"

The late great Mike Dickin had the best response this question; he always said, "My health is not in question"!

There's one guy where everyone works who says that. And there's always one woman with a 'you don't have to be mad to work here, but it helps!' mug.

if you know what it means it`s making sense.

If someone says 'Good morning', do you get confused because you think they're telling you that the morning has been well behaved?

Seriously, do people imagine that 'good' has only one specific meaning (i.e. 'well behaved')?

I'll start reeling off a long list of real and imaginary ailments until they wish they'd never asked. When you think about it, it's such a pointless thing to ask because it's nearly always a reflex action without any thought going into it. I've actually just said hello to people and had them reply 'I'm okay thanks', or similar.

Personally, I say, I am fine thanks, are you? Regardless of whether I am fine or not