I've always learnt at school that we have to say: "You were + (add something)" either if the "you" is actually one person or more. But sometimes I heard or read "You was + (add something)" especially in some video games.
I remember that I saw it in a custom mod on Final Fantasy 7 on PC for example. But I've even heard some people say it, but those people were friendly between them.
I can't remember the sentence from FF7, but the words of the sentence were pretty much mashed. An example here though: "You was behind us the whole time". That sentence was said by a nice, yet random guy from an online game, I asked him if that was correct to say that, he said yes (but I wanted to confirm that).
So I was wondering if that is correct? Or is it a kind of a common -I would say- speaking mistake?