1. Return Receipts on emails when used as a manipulation technique. Sure, they're great if you want to make sure that your professor received your final paper or your boss has read your status report, but they're incredibly annoying when people use them to harass you, as in "I see that you read my email 10 minutes ago. Why have you not responded to my long and detailed question, the answer to which I am too lazy to research for myself?"
2. When people can't quite grasp the concept of personal space.
3. Drivers who go five miles below the speed limit in the left lane. It's called the passing lane for a reason, buddy.
4. Bad grammar.
5. PeEpLez wHo tYPe lyKe dIs bEcUZ tHaY lYkE 2 buTcHeR DA eNGlIsh lAnGuAge.
6. People who interrupt a lot. Here's how polite conversation works: First, you say something. When you're finished, I say something back. After I've stopped talking, you respond. Serial interrupters are welcome to write that information on their hands for future reference.
7. When a book's back cover or book jacket gives away a part of the story. For example, on the back cover of the book I am currently reading, it says that the daughter of one of the main characters is "involved with a young priest." I am currently on page 250 of the book, and so far the daughter is kind of weirded out by the young priest and tries to avoid him. But thanks to the back of the book, I know that they're going to become "involved," and it annoys me that I already know that. Stupid spoiler book cover.
Add your own to the list - it's fun to complain about things that you cannot, realistically, do anything about!