In Deep Southern, "y'all" is -never- used as a singular. :)
Well, as I said, I'm a hillbilly from the Ozarks. ;-D
Another one I've heard as an exclamation: "Well, s--t far (fire) and save matches!"
Someone should note that the proper initial salutation in Georgia is "Hey". Only after an exchange of "Hey's" can one use "Y'all" or discuss trucks and dogs. Of course, when addressing elders or managers the formal tense is used such as "Hey mister Pruitt" etc.