Christmas is a time for chestnuts and I've been musing on this old one...
"If you're planning to go to the party wearing that, you've got another..."
...think coming
OR
...thing coming
?
The facts appear to be that "think" was in the original phrase, but - rightly or wrongly - "thing" is well-established as an alternative:
"Another think coming" - examples have been found from before 1900: itre.cis.upenn.edu/~myl/languagelog/archives/004972.html
"Another thing coming" - example exists from 1919: itre.cis.upenn.edu/~myl/languagelog/archives/004971.html
As that second link (written by an academic linguist) mentions, the OED sees "thing" as a misapprehension of "think", but both seem popular.
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Arguments I've heard on either side plus my response:
"another think coming" doesn't make sense / think is a verb --> 'think' can be a noun, you could be saying "if you think that you are going out dressed like that, then what is coming to you is some time where you will need to sit down and have another think (until you change your mind)", "Have a good think about this" - 'think' is a noun.
"think coming" isn't easy to say, the 'k' and 'c' clash --> yes, but that doesn't mean it's not a valid phrase, but it probably does explain the mishearing or preference for "thing coming"
"another thing coming" doesn't make sense - what "thing"? if it's "another", what's the first "thing" --> lots of idiomatic phrases are hard to make sense of when you try to analyse them (I thought of "sick as a parrot" off the top of my head - but parrots aren't sick? oh, and actually, what on earth is the sense of "off the top of my head"?). There's enough sense for people to use it: "if this is the thing that you are planning to do, then you are mistaken, and you will soon discover that there is another (different) thing that you will be doing [ thing that will be happening to you]".
But everyone I know says "think" / everyone I know says "thing" / it's what I've always said --> are you sure that's what everyone is saying because it's hard to distinguish in spoken English? For most of my life, I just naturally thought it was "thing", and now I'm convinced the 'correct' version is "think", but I'm not too fussed about "thing" as it is so common.
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I was amused when years ago, David Cameron used it in a speech, and two separate articles in The Telegraph quoted him, one writing "thing" and one "think" (unfortunately, I've searched and can no longer find the articles).
So, you can go on fighting for your choice and insist that logic is on your side. Personally, I just appreciate the way both have been accepted and I enjoy it when people discover the other version for the first time. AIBU?
YABU = you need to pick a side
YANBU = agree, let both thrive