When you meet a Texan on the street, and even if you don’t know him or her, thye are friendly and familiar and will ask you, “How y’all doing today?c
It is fact.
Y’all is singular, all y’all is plural.
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My PaPaw used to wave at everyone he drove by. They didn’t always wave back...I never thought about how sad that was until I was well into my thirties...
We retired to a semi-rural area on the Maryland Eastern Shore. Among the many things I love about this area is that people here do that wave to everyone. Didn’t take long for us to begin this lovely custom.