I don't think that yous should be refered to as 'slang'. It is a dialect form common across much of England and Ireland. I doubt that it particularly originated in Ireland at all, particularly as it is in use in the West Country which is the 'mother' English dialect of Hiberno-English.
I don't think the term "yous" is necessarily slang. Consider the following sentence (which I wrote myself for a philosophy essay on parallel universes):
- In each universe there is an I, and there is also a you. And these two Is are exactly the same, as are also these two yous.
Whether or not my use of "yous" in that sentence is good English style or not, I would scarcely call it slang. Although in my essay it is a slightly different plural from the usual plural of "yous", since in normal use it functions as addressing a plurality of person, whereas in this case it is addressing a single person, the reader, yet addressing a plurality of putative instances of them across multiple parallel universes.
I think that as thou-you has decayed into you-you, it is only natural that a you-yous distinction has begun to evolve to take its place. (Thou-you decayed because plurality was hijacked for a T-V distinction, and as the T-V distinction decayed plurality did with it. But, I think given the nature of modern society, if the singular/plural distinction re-emerges in the form of you-yous, it will not decay again, because we are unlikely to see the re-emergence of T-V in English.) At the moment I would say that "yous" is not exactly standard, but is not entirely incorrect either. Only time will tell how far this evolution goes, and whether "yous" remains in its current status as on the fringes of standard English, or becomes a fully standard part of our language.--184.108.40.206 03:05, 20 April 2008 (UTC)
Related news column
By an Irish journalist : http://www.irishtimes.com/culture/heritage/the-correct-youse-of-english-1.1623440 . Gronky (talk) 02:26, 11 December 2013 (UTC)