For those grammar mistakes that make you die a little inside every time you see them.
I am not a Grammar Nazi. My grammar suffers on occasion too. But the utter stupidity of a comment like "your stupid" makes me cringe. It's even worse to see it in a piece of literature. You should always publish only your best work, and a piece of literature with terrible grammar is not one's best work. So here's a quick refresher course on some of the most common grammar mistakes.