The worst offenders on Facebook are the thread hijackers. You know them. You post a seemingly innocuous statement about loving baseball, and one of them comments how he and his girl went to last week's Yankees game and had soooo much fun. Before you know it, she's chiming in about how they always have so much fun because he's SUCH a blast, and they've turned the thread into a mutual gush-fest, seemingly unaware of everyone else on the Internet.
Not only is this rude, it's gross. Even if you're going back and forth complimenting one another (or talking about your date last night) on your own wall, the conversation is still very public. Plus, we know you two live together and are on your laptops while in the same room. Get off the damn computer and talk to one another, and leave all of us innocent bystanders out of the conversation.