I thought the phrase was, "if you think... you've got another think coming.", but no:
http://www.comics.com/comics/pearls/archive/pearls-20040724.html

Cannot imagine that the cartoon is correct. I've never seen that, and I figger I'm old enough to have seen darned near everything!

I've always heard "thing". always figured that "another think coming" was a clever play on words... huh.

"If you think that, you have another think coming" means "You are
mistaken and will soon have to alter your opinion". This is now
sometimes heard with "thing" in place of "think", but "think" is the
older version. Eric Partridge, in _A Dictionary of Catch Phrases_,
gives the phrase as "you have another guess coming", "US: since the
1920s, if not a decade or two earlier". Clearly "think" is closer
to "guess" than "thing" is. The OED gives a citation with "think"
from 1937, and no evidence for "thing". Merriam-Webster Editorial
Department writes: "When an informal poll was conducted here at
Merriam-Webster, about 60% of our editors favored 'thing' over
'think,' a result that runs counter to our written evidence."



Source: [Mark Israel, 'Phrase Origins: "You have another think coming"', The alt.usage.english FAQ file,(line 5502), (29 Sept 1997)]


http://www.yaelf.com/aueFAQ/mifyuhvnrthnkcmng.shtml

guess I should be an M-W editor...

think, n.
2. a. What one thinks about something; an opinion.

1835 LADY GRANVILLE Lett. (1894) II. 187 My own private think is that he will execute another voluntary. 1861 J. BROWN Horæ Subs. Ser. II. 355 The cobbler..dispenses his ‘think’..to all comers on all subjects.



b. to have another think coming: to be greatly mistaken.

1937 Amer. Speech XII. 317/1 Several different statements used for the same ideathat of some one's making a mistake...[e.g.] you have another think coming. 1942 T. BAILEY Pink Camellia xxvii. 199 If you think you can get me out of Gaywood, you have another think coming. 1979 Jrnl. R. Soc. Arts CXXVII. 221/2 Any design consultant who thinks he is going to get British Leyland right by himself on his own has got another think coming.
[OED2]

you don't find think as a noun very often...

...and I'll be your dissenting opinion!

"noun
1. colloq
An act of thinking.
Example: have a good think"

http://www.allwords.com/word-think+twice.html

see, it's one of them colloqs...

The Colloq People lived a peaceable and happy existence in what would later become the United States, until the advent of the white settlers challenged their simple way of living and communicating. They not only had no written language (they were pre-scriptivists, in this sense), but they had no rules of grammar nor syntax, as well. Everyone was allowed to use words any way they liked and to mean anything they liked, so long as one other person agreed that she or he understood the speaker's intent. When missionaries attempted to teach them English, they developed the notion that their own language was primitive and required rules but were so confused by the effort that their language and eventually their culture died out.

you done did thunk it out, Padre!

I don't think it died out completely. There must have been some escapees...perhaps hidden in caves, who surfaced later. Else, how to account for "the floors need washed", "my hair needs cut", "this screed needs writ", and "throw the cow over the fence some hay"?

"throw the cow over the fence some hay"?

I saw that episode of Northern Exposure.
Episode 29. "Burning Down The House" (2/3/92)

Cave ne ante ullas catapultas ambules.

Another think coming vs. another thing coming was discussed at length on another forum recently. Since it was discussed at length I'm thinking it was ezboard wordorigins. But then I may have another think/thing coming.

ezboard wordorigins

It was, indeed, ezboard wordorigins. Unfortunately, the ezboard search function is worthless so it's almost impossible to find anything on that board. Sometimes googling 'phrase-of-interest wordorigins' works, but not this time.

I've always heard "another thing coming" too.

Haven't we discussed this here, somewhere in the distant past? Being wholly inadequate at finding anything with the search function, I'll leave it up to our expert trackers to find it.

>Haven't we discussed this here, somewhere in the distant past?

I thought so too, but my prepostal search didn't find anything (other than 1 instance of "another thing coming" posted by oftroy).

...prepostal search ...

Is the antonym of prepostal postpostal?