I wish I was joking. And I realize those videos are edited for dramatic effect BUT.
They're, there and their are always mistaken, one for the other, as one example.
To be fair, I catch myself in this one fairly often, and probably do it without noticing a fair bit. It can be more of an autopilot thing than a stupidity thing. We're still spelling English approximately as it was pronounced 6 or 8 hundred years ago, even though the pronounciation has changed significantly. So we don't really have a user-friendly encoding scheme to begin with. "There" and "their" ought to be merged in spelling (after all, we get along just fine with all the different words pronounced "bank" spelled the same. You have river banks, financial banks, and the bank of an airplane making a turn). "They're" could be merged with the others or not, depending on how distinct you want to make contractions.
BTW: My mom just caught me spelling "led" (as in the past tense of "to lead") as "lead" (as in the metal). Point being that it's not just stupid people that make spelling errors.
Ask anyone at random where France is on the map (or any place at all) and watch them not find it for a long while if ever...
That's a bit more concerning.
Ask them what constitutes the US congress and watch them say "I don't like/follow/understand/care about/need to know, etc... any thing about "politics".
Scary, but at times the behavior of politicians does make it hard to blame them.
Ask any one what an adverb is...
If I'd gone into astrophysics like I wanted to as a kid, I'm not sure I'd have cared enough to be able to tell you now. But then I got hooked on foreign languages and linguistics, and in that line of work it's kinda hard not to know.
What the name of their state governor is...
Rick Perry.
What difference exist between syrup and sugar...
Depends what exact definitions you want to use. Most could tell you the difference between pancake syrup and table sugar (color, liquid vs. solid, etc.), few could tell you the difference between lactose and high fructose corn syrup.
Even professional astronomers weren't entirely sure before the 1920's.
What is compound interest...
Given American credit-happiness, this is the really scary one.
In almost all fields, except sports, most Americans are without a clue.
There are a few gems that carry the rest of us along towards a future... But few indeed.
More than you think. But all too few.