The expression i'm in or count me in mean that you wish to be included in a proposed activity I'm going to the bar Anyone else coming? count me in! i believe the expression may originate from gambling, possibly poker, or some other card game where players are dealt a hand and then decide whether they are playing on by saying that they are either in or out The meaning of the prefixes is the same (negation the adverb), but they are still different prefixes. The phrase who's in? does exist in very informal english, at least in american english It is equivalent to saying who wants to participate in x with me? it is not used very often, at least in my experience
However, people will understand what it means if you say it in conversation For example, if you wanted to get food I'm feeling hungry, so i'm going to order pizza According to the cambridge dictionary, on it means informally doing something that needs to be done, or trying to solve a problem In my experience it doesn't imply one or the other In fact, the joke is that when your boss asks you how something is coming along and you say don't worry, i'm on it, it could both be interpreted to mean that you'll start immediately but also that you were.
I am from india and not a native english speaker I do often hear people introducing themselves like hello everyone This is james is it an acceptable form in native english I am on it in your first example sounds like a shortened version of i’m on the case, a colloquial way of saying that the speaker is dealing with it In the context of some kind of dispute, as in your second example, they’re at it again means that they have started doing again whatever it was that was a component in the dispute. Is it common to say i'm game in place of i'm in or count me in
Is it used often in american english?
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