I have a wide variety of pet peeves, but I think my biggest one is the disregard that today's society has for proper grammar and correct spelling. On social networking sites such as Twitter and Facebook, I am ambushed by people not knowing the difference between "your" and "you're," "to" and "too," "they're," "there," and "their." The fact that texting lingo has made it acceptable to substitute "ur" for "your" or "you're" made it incredibly easy for everyone to fall out of the practice of using proper spelling. As I run down my Twitter timeline, I see that people attending college are spelling like they have never picked up a book before and it really makes me shudder.
I think the thing that bothers me most is the fact that all these misspellings and grammar mistakes don't bother the people making them. "This ain't an English class" and "People that correct my spelling are annoying" are tweets that often come up on my timeline. True, they won't be getting graded on their tweets, but if they are making those mistakes on their everyday posts, the chances that they will be making them on things that actually matter are much greater.
I'll leave you with these final words of wisdom: spell-check, people!