RB> Where have I mentioned "good language"?

Joe>   For me, it was an inherent statement in your argument. I do hear
Joe> _vernacular_ Anglophones saying "ain't do nothing". If they use it,
Joe> it have to be English.

No, you have misinterpreted Ray's comment for the third time.
He was not prescribing.  He was saying that "ain't do nothing" does not,
in his experience, occur in *any* variety of English, no matter how
vernacular or idiomatic or nonstandard or whatever.

I would agree with Ray on that point.  The phrase "ain't do nothing"
is nonsense in my 'lect - not because it's "formally" wrong, not
because it's "improper grammar"; it simply makes no sense, at a
fundamental level.  Nor have I personally heard it in other dialects.

Note what we're *not* talking about: things like the fact that in formal
English, the very word "ain't" is disallowed.  That's not what's under
discussion here.  The related phrase "ain't doing nothing" is perfectly
good English in any number of dialects, including my everyday register.
But what I gather to be the intended meaning of "ain't do nothing" would
normally be "ain't gonna do nothing" or "won't do nothing" or some such.
I'm not sure because, as I said, the phrase is meaningless to me; I have
a hard time even imagining what it is supposed to mean.

Now, Mr. Cowan notes that the phrase occurs in AAVE.  In that case,
Ray happens to have been mistaken, just as I would have been if I had
been the one who posted the message, which I can easily imagine.
But saying that he was mistaken is not the same as saying that
he was making a value judgement.