But then you change the meaning of the sentence. Sure, I can add words to any sentence to turn it into a thought-based expression rather than an action-based one. But that's not the point.

Here, there's no implication of thought. He can think all he wants about coming into work late, and there are no repercussions of doing so. Your sentence turns it into him not thinking something anymore. My original sentence does not deal with any thoughts, only actions. The thing that has repercussions is his action (of continuously arriving late), and that's the only inference you're to draw from it.

So I'm pretty big on correcting other people's grammar when they misspeak. A coworker recently pulled up a website with "things people often mistakingly say" (notice the use of 'mistakingly' instead of 'mistakenly', how funny of them!). Anyway, the only one on that website I hadn't heard before was the one being discussed here. It's always been "thing" to me. And why not - it makes the most sense of the two!

I know this has been touched on already, but 'think' is not a noun people! Some verbs can also be nouns, sure. Like 'bite': it can be 'to bite', or 'a bite'. But you can't do the same thing with 'think'. You people keep saying "have a think", and I'm sorry but you just sound ignorant. Perhaps that's okay in the UK, but you sound like a fool saying something like that in the US. The corresponding noun for "think" is "thought". You have a thought, you don't have a think.

So, in that respect if indeed the original idiom was "you have another think coming", it makes absolutely zero grammatical sense and should have instead been "you have another thought coming". THAT, I can see being the correct phrase; but not with "thing". I understand that's the way it's been, but that's not to say it's completely ludicrous.

Someone also brought up the point that the phrase "you've got another thing coming" is not always (and actually more-often-than-not) preceded by "if that's what you think" or "if you think that". Someone else said that the example of "if you expect that to happen..." is not a good example because you can translate "expect" to "think". Well, in my experience it is not a thought or expectation that causes the phrase to be uttered. Consider this:

Bill is an exceptional worker, but he is often late for work. But Bill just got promoted to be a manager. Upon promoting Bill, his boss says "Bill, I'd like you to be the new manager. But if you keep coming in late to work, you've got another thing coming."

Now explain to me how "think" could make any logical sense in this case? Bill has something coming to him (a good thing - the promotion), but if he keeps his bad habits, he'll have something else entirely coming his way (a bad thing - he'll be fired).

Ready, go.