Another think coming
To have 'another think coming' is to be greatly mistaken. The phrase is usually spoken by an antagonist as 'you have another think coming'; the implication being that one will shortly be obliged to adopt a different viewpoint, either by the presentation of indisputable evidence, or by force.
I'm going to have a little think here. My first thought is, "is it worth embarking on a piece that discredits the 'another thing coming' version of this expression"? Many people use that version, in fact it is much more widely used than the original and correct 'another think coming' - and I know I will get emails. Such emails usually come from people who present no evidence whatever, but KNOW THEY ARE RIGHT. Nevertheless, let's press on.
You might think that 'think' should be 'thing'. Well, you're wrong.
The most compelling argument in support of the view that 'another think coming' is the original text of this expression is the fact that it pre-dates 'another thing coming' in printed citations. While 'another', 'thing' and 'coming' are very common words and occur together in print in some early documents, they never do so with the 'mistaken' meaning of this phrase, but only in examples like 'one thing was coming along the road; followed by another thing, coming afterwards', or similar. The earliest real example of the 'thing' version of the phrase that I've found is from the New York newspaper The Syracuse Herald, August 1919:
"If you think the life of a movie star is all sunshine and flowers you've got another thing coming."
The paper's local rival, The Syracuse Standard, outdoes that by several years, by printing the 'think' version in May 1898:
"Conroy lives in Troy and thinks he is a coming fighter. This gentleman has another think coming. It is probable that McCoy will next meet Joe Choynski."
'Another thing coming' is just a mispronunciation of the original phrase. The source of this mistake is probably the duplicated 'k' sounds of 'think' and 'coming'. When voicing 'another think coming' the two 'k' sounds are merged and what we utter phonetically is 'thingkumming'. There's very little difference in sound between that and 'thing coming'. The 'thing coming' speakers may also have been influenced by a sneaking feeling that 'another think coming' is ungrammatical. Actually, a little consideration shows that it is perfectly grammatical, although it is a rather unusual form of speech - we would normally use the word 'thought' in this context. The split-second choice of how to pronounce a word doesn't give time for such considerations and many people have just opted for 'thing'.
Another reason that 'thing' is incorrect, and perhaps this should have come first, is that 'another thing coming' makes no sense. How can one have another thing coming where there is no first thing? In order for 'thing' to make any sense we would have to say 'if you thing that, you have another thing coming', or 'if you think that, you have a thing coming'. Nobody says either of these. Case proven, in my humble opinion.
Please, if you are thinking of emailing in support of 'another thing coming', have another think and then gather your evidence.