Incorrectly using 'of' as in "shouldn't of done that" or "I would of done that if I'd remembered".
I know why people think that's how it's written. Because that's what it
sounds like. Granted, 'shouldn't've' is a double contraction, which is
considered non-standard. But that's no excuse. That just means you
shouldn't use it when writing in the first place. 'Would've' has no such
excuse. The person who gets that wrong didn't pay attention in English
class or they never learned it in the first place.
When I see this I really feel like there just isn't enough attention given to education in the U.S. And I'm not even just talking about money. I'm talking about respect. Lack of funding is just a symptom, not the disease itself. The disease is how little Americans care of learning. They like to keep it real instead. There's this attitude here of "Too much book learning will make you lose sight of how the real world works."