In the past I’ve been asked to explain the meaning of “all y’all” (or “all of y’all” if you’re feeling fancy).
“All y’all” is the Southern Inclusive Plural — specifically, it means *all of you,* as opposed to “y’all”, which means “you (plural)”.
“Do y’all want to go to the movies?” means “Do you (plural) want to go the movies” and *doesn’t* require everyone’s response, as it’s a general “any of the you’s who are assembled here”.
“Do all of y’all want to go to the movies?” on the other hand, is asking if there’s a *collective desire” to attend the movies.
In my experience “all of y’all” is particularly useful when, for instance, you’re at a larger gathering at which you only know a subset of people.You don’t know everyone, but you want to indicate that everyone (even those folks whose acquaintance you haven’t yet had the pleasure of making) is included in an invitation.
“Hey — there’s a movie in the park in an hour. Do all y’all want to go?” The implication is that I’m suggesting that after we’re all done eating dinner at the restaurant, I’d be delighted if we *all* adjourned to the movie in the park. It avoids the situation where few of us are heading in one direction as we are leaving and someone else asks “Where are y’all going?”, leaving one of us to answer “To the movie in the park…” […that we didn’t tell you about…] Awkward, and totally avoidable with “all ya’ll.”
The converse is equally useful:
When speaking to the three people at a party with whom one carpooled, and requesting departure from said party, “Are y’all ready to leave?” means “are you, the people whose conveyance I shared, ready to go?” not “is everyone at the party ready to leave” (with its inherent implications that the Party is Over).
(“All y’all” is written as such, but pronounced “alla y’all”. This oughtn’t be surprising, as much of Southern would look the same if written phonetically ;-)