Re: Are these Sentences Grammatically Wrong??
I consider the real/terrible examples wrong on any type of exam or in any type of writing more formal than an email to your friends. I don't speak that way, my children don't speak that way, and my colleagues don't speak that way.
While we are losing the subjunctive in sentences like "If he was serious" instead of "If he were serious," I have never heard anyone, American or others, say "If I was you." Ever. Are you sure you've heard that? Or could it have been "he was" statements instead?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.