Pet Peeve of the Week: The Difference Between "Seen" and "Saw"

I don't know if this is a common grammar issue all over the place or just where I'm from. I'm going to bet its everywhere. Now, I know that English is a stupid language. (This is a common thing found all over the internet but here's a link to the first blog I found. Hilarious, give it a read.) Anyway, the thing that baffles me is that people can't get their minds around the difference between "seen" and "saw." *disgruntled sounds*

The number of times I have heard "I seen that movie," I don't even know.

"I saw that movie," or, "I have seen that movie."
"David saw me at the park," or, "David has seen me at the park."

OR

"Have you saw that movie?" NO!

"Have you seen that movie?" Yes.

Now, I'm not an English teacher, so maybe I'm wrong, but how about we make a rule that "seen" can't be by itself? "Has" or "have" need to go with it. They're best friends, attached at the hip. But "saw" has no friends and should be all alone.

Or, I read this somewhere, and it made sense to me:
Think of the use of "seen" as talking about the past, but thinking about the present.
Think of the use of "saw" as talking about the past and thinking about the past.

I understand that this may be extremely confusing so let me put it this way:
"I seen you yesterday," doesn't even sound right!! Or is that just me? I understand that maybe some people just never learned it, or they never quite understood it, but I honestly don't think it's a concept that is too difficult. And maybe it's habit now. That's understandable as well. But bad habits can be broken. So let's break them before I start breaking things over the heads of these grammar murderers.

I will admit, I am an unofficial member of the infamous Grammar Nazis (although I hate the name. I would prefer Grammar Angels or something nice like that.) But someone has to be in charge of this stuff. You can't just go making your own rules about language. Wait, that's not a hundred percent true. If you know what you're doing (kind of) there's possibility for some creativity in language. But it's a different thing if you're doing it on purpose, right? Do I sound like an a**hole? Yeah, probably a little bit, but that's just how much this grammar mistake rattles me.

This doesn't mean I don't make grammar mistakes myself. I do it all the time. But I'm also constantly looking up the proper way to say things because I don't want to write posts like this and have people call me out on grammar mistakes that I've made.

I don't have anything to say to sum this up. Just stop doing it, okay? Just stop!