If you just wrap the sentence in quotation marks, all is well:
"This is a great big smile" is my official story.
The NP my official story naturally refers to a linguistic entity. That approach doesn't work with the predicate is what's happening because what's happening doesn't (ordinarily) refer to a linguistic entity.
I've used that type of formation around people from England to South Carolina, and Louisiana to Oregon, and I've been told it sounds weird. It led me to think at one point that it could just be a Michigan/Midwest thing, since I'm from Grand Rapids. And now I come to find out the author of this comic is from Lansing and worked as a journalist in Grand Rapids.
A stickler might ask for an added "that" to convert the thing into a NP. ("That this is a great big smile is my official story.") Come to think of it, the same stickler might ask for the same sort of modification of the two direct objects of "tells". ("… tells me that you rode …", "tells me that you had …")
This usage seems very Pynchonian to me. The only one I can find currently is:
But a hardon, that's either there, or it isn't. Binary, elegant. The job of observing it can even be done by a student.
Unconditioned stimulus = stroking penis with antiseptic cotton swab.
Unconditioned response = hardon.
Conditioned stimulus = x.
Conditioned response = hardon whenever x is present, stroking is no longer necessary, all you need is that x.
Uh, x? well, what's x? Why, it's the famous "Mystery Stimulus" that's fascinated generations of behavioral-psychology students, is what it is.
@Tom Saylor said: If you just wrap the sentence in quotation marks, all is well
Yes, but I don't think this is just missing quotation marks. Which of the following can "his official story is that he shot the sheriff" be expressed as?
1. I shot the sheriff, is his official story.
2. He shot the sheriff, is his official story.
I'm not a native English speaker, so I can't quite tell, but I suspect 2 is grammatical (for people where the original sentence under discussion is grammatical), so that cannot be direct quotation. Some kind of indirect quotation, maybe.
@Adam Roberts: 'It's an Escher pattern, is what it is.'
Not sure that this is the same phenomenon. At least this is almost definitely not a case of a sentence as a subject. If "It's an Escher pattern" were indeed the subject of this inverted pseudo-cleft, we should be able to transform it to "it is 'it's an Escher pattern'", which seems suspect.
@Usually Dainichi: Surely if ‘It’s an Escher pattern, is what it is’ is an inverted pseudocleft (which it surely is), then the corresponding (non-inverted) pseudocleft (which is acceptable for me) is ‘What it is, is it’s an Escher pattern’.
What this seems to have in common with the original ‘This is a great big smile, is my official story’ (or its inverse, ‘My official story is, this is a great big smile’) is that both patterns, unlike ordinary it-clefts, for instance, have on one side of the copula a (possibly elliptical) answer to an implied question on the other side of the copula. It’s not clear to me what conditions license this kind of copular construction in general, though. Question–answer structures are involved somehow, is my tentative explanation.
1. I take back my comment that people don't talk like that – someone from North Carolina has just told me that where she lives, it's very normal usage. Often the ending would be "is the thing", e.g.
He wasn't being rude when he declined our invitation. He'd already eaten, is the thing.
which strikes me as an alternative phrasing to "that's the thing" – so the "that" is omitted.
2. I think @Usually Dainichi makes a good point about the sentence-acting-as-subject not always being a quotation, so quotation marks won't always work. My inner pedant really wants quotation marks to work for this, but since this seems very casual usage in informal speech, I think it makes sense that the punctuation is a bit casual and informal.
The funny thing is, while I was away from my desk I thought of this very construction as possibly being another one of those question–answer uses of the copula. But @Meirav M. (Berale) beat me to it, is the thing. (OK, I wouldn’t normally say or write a sentence like that second one, but I don’t have a big problem with it – and my first sentence is perfectly ordinary, I think.)
I had a colleague who used to say, "So the question becomes, is [state new question here]". I always had trouble parsing it. I had a strong sense that "is" was not meant to be simply in apposition with "becomes". It's not quite sentence-as-subject as in the Frazz comic, but it may be an idiosyncratic variation on it.
The current edition of the Haverford College alumni magazine has an article about an alum who is teaching in an urban middle school. A student is quoted as saying:
"Him thinking we are up to the challenge makes us believe that we are."
This seems perfectly grammatical to me, but I can't figure out why.