People who are anal-retentive over grammar and habitually correct wrong usage.
Our biggest grammatical pet peeve by far is the mistakenly possessive "it's." But then again, we also think everyone should just talk in LOLcat-speak.
Editorial note: Whoa! You've found a super-old post here on BuzzFeed, from an earlier era of the site. It doesn't really represent where we are anymore, and may in fact be totally broken, but we're leaving it up as a part of our early history.