@Vincent Berg
I'd almost suggest using a footnote to denote: "usage may vary in different locales". :(
I originally asked a question about an expression (you know) and not y'all. After aubie convinced me not to use it in the singular, I looked it up on Wikipedia and now I'm convinced he was right.
There is long-standing disagreement about whether y'all has primarily or exclusively plural reference.[4] The debate itself extends to the late nineteenth century, and has often been repeated since.[10] While many Southerners hold that y'all is only properly used as a plural pronoun, strong counter evidence suggests that the word is also used with a singular reference,[2][9][12][13] particularly amongst non-Southerners.[14]
Notice the "non-Southerners" which is me. I didn't want to come across as stupid in my story.
and
H. L. Mencken recognized that y'all or you-all will usually have a plural reference, but acknowledged singular reference use has been observed. He stated that plural use is a cardinal article of faith in the South. ... Nevertheless, it has been questioned very often, and with a considerable showing of evidence. Ninety-nine times out of a hundred, to be sure, you-all indicates a plural, implicit if not explicit, and thus means, when addressed to a single person, 'you and your folks' or the like, but the hundredth time it is impossible to discover any such extension of meaning.
— H. L. Mencken, The American Language Supplement 2: An Inquiry into the Development of English in the United States, 1948, p.337
Note the "he stated that plural use is a cardinal article of faith in the South" and "ninety-nine times out of a hundred, to be sure, you-all indicates a plural."
So I took it out of the story.
