Hahahahaha! Ha... no.. really. That's so sad it's funny.

I know plenty of "Amurkins" who can't speak or write the only language they "know". Foreign speakers/writers these days are easier to pick out not for poor grammar, but for the proper yet uncommon use of words like whom or whilst. If it has more than two syllables or any rules pertaining to when it's proper to use it, it's generally misused or avoided all together. Don't even get me started on things like its vs it's, effect vs affect, or their, there and they're.

True story from a college professor friend: The topic of "Nature vs. Nurture" came up for discussion in class. One kid kept going off on bizarre tangents, saying things like "This is stupid to talk about; there aren't even that many test-tube babies out there!" After class, the student approached him and asked, "What's a nurture anyways?"

Do you see every sentence beginning or ending with an eh? If you did, maybe he'd be Canadian, eh? But really... Canadians have slightly different inflections (toward but not quite French), but generally their English is better than most Americans.

Hey now... There are plenty of skinny Americans. In my travels, I've seen plenty of... "heavy set" folks all around the world. Do you think this woman or this child are Americans? (Yes, I googled McDonalds and "fat" in a couple languages...)

Over all though, most US English speakers are quite tolerant of language gaffs. Unless you confuse the word order, then they tend to not get anything you're saying. But that's true of most languages.