ANY status update that contains the words, "97% of people won't repost this..." Passive aggressive, much?
People who post things that are totally inflammatory and/or blatantly untrue, that a simple google search would debunk. And if you point it out, they freak out and act like you're being unreasonable. (For instance, a friend of mine posted that drinking soda will cause you to develop osteoporosis, so you shouldn't drink any soda, ever. Mmmkay, that will only happen if you drink so much of it that you develop acidosis, at which point osteoporosis is the LEAST of your worries!)
People who post cryptic, drama-filled status updates, but then won't explain what they're talking about. I have to think, if you're THAT upset with someone, why not just send them an e-mail or private message? Do you really accomplish anything by posting, "I hate when people tell you they're your friend, and then they backstab you and betray you!" No kidding? Because I'm sure most of us *love* people like that. :-/
People who constantly post pictures of their dinner (lunch, breakfast, latte, etc). Once in a while I don't mind, or if they're at a really great restaurant or whatever, but every day? Seriously?! Yeah, your tuna casserole looks awesome. I'm sure yesterday's spaghetti was equally wonderful. Nobody cares.