This is an interesting thread. I was exempted from English classes in seventh and eighth grades because my skills were considered advanced, so I had an "independent study" period instead. I
still wonder what I missed during those years!
Several of my pet peeves have been mentioned. The misused words/phrases that irritate me most are:
it's / its
you're / your
affect / effect
complement / compliment
their / they're
principle / principal
would/should/could
of / would/should could
have (correct)
1920's / 1920s (correct)
sentences ending in prepositions (exceptions might be dialogue)
I have never used
Garner's Modern American Usage. That looks like a book I'd enjoy reading cover to cover! I'm such a word geek, and I enjoy learning.
I don't correct people when they mis-speak, but I certainly have been tempted to mark up incorrect advertising signs! And when there are too many errors in a book, it completely ruins the story for me.
I'm
not perfect, though. I sometimes struggle with elements of grammar and sentence structure. In many cases, I suspect that something
might be wrong, but I'm not always sure what
is correct.