Hairy, 'fine' is merely a single word utterance, not a sentence, by your wife. It is so often the final word in a 'discussion' with a wife. This is in contrast to 'I do', which IS a sentence... a life sentence at that.

Heather, IMO, bathroom is no funnier than restroom. I know when I go a public bathroom or restroom, I don't bathe or rest... it's all business!

Brus, are you sure that American pupil wasn't Canadian? 'Bathroom' is the common term used here in Canada. In my frequent visits to the US, I have noticed that 'restroom' is the prevalent term there.

JJMB, your responses are laughable. Again, you have failed to give YOUR reasons why 'fine' and 'sure' are sentences, besides the fact that you say so. You have merely put down my and other posters' responses or asked more questions. You have waved off dictionary meanings and definitions from structural grammar. Lastly, you have dissed 'the father of modern linguistics'. By the way, did it take you so long to figure out who Chomsky was? I guess we will have to wait till YOUR book comes out to find out YOUR theories on grammar.
I will not reply to another post from you until you have something thoughtful or credible to offer to the original question.

Yes, (that is) exactly (right).
The omitted words can be inferred, as I explained to JJMB. Perhaps he has not reached that higher level of thinking yet? lol.

OK, JJMB, you don't like the definition of a sentence in structural grammar. The dictionary meaning is too simplistic for you. Tell me then how Chomsky would explain 'fine', 'sure', and 'shit' in TG terms. What are their deep structure? Show me their tree diagrams.
Or are Chomsky's rules too 'petty and contrived' too?

Well, Professor, you still fail to enlighten me as to WHY 'fine', 'sure', 'done', and 'there' are complete sentences then, if you discard the context explanation (you make no mention of the inferred/understood explanation). And back it up with some sources, would you? You merely deride my explanation without offering your own. I didn't claim to have a higher level of language than you, though like you, I did take Latin 101.
'Shit' is not a sentence, but merely an interjection, much like 'ouch' or 'wow'.
'Language is too expressive to be contained by petty and contrived regulations.'
But they are necessary. Language anarchist, are you? You're probably one of those who not only approve of, but say 'If you need help, just call my wife and I.'

Professor Ballantyne is strangely silent. Please enlighten us as to WHY you think 'fine', 'sure', and 'surely not' ARE sentences. Perhaps you come from the same 'because I say so' school of grammar you accuse me of coming from? Or is it that other school of 'I see it so it must be true'. LOL.
Have you not progressed beyond the basic level of language use of single words and phrases? :)

I call my shithouse my 'log cabin'. The urinal is the well.

Out here in BC, Canada, I have only heard Sco-sha as you say.
'Scothia'? I would say this girl has a lisp!