I want to talk about the word: Y'all

It's a contraction of "you" and "all". A distinctly southern/country thing.

But is it "proper" or "formal" english?

I think it's informal and grammatically incorrect. I think that "you" is both singular and plural and if you feel the need to pluralize "you" in formal writing, you should probably find a different way to say it than to add in "all", whether contracted or not. But I've been told I'm being stupid.

Am I stupid?