What's the proper etiquette for unfriending someone on Facebook or similar sites? Do you tell them why? Keep it quiet? Just stay friends?

Mark your calendars, Facebook masses. November 17 is National Unfriend Day, as declared by late-night talk show host Jimmy Kimmel. "Friendship is a sacred thing, and I believe Facebook is cheapening it," he says.

So Kimmel suggests examining your list of Facebook friends and only keeping the real friends (you know, as in people who've actually breathed the same air as you). Good idea, Mr. Kimmel. According to Robin Dunbar, a professor of anthropology at Oxford University, our brains can't keep up with more than 150 friends anyhow.

So, why not? Go ahead and use National Unfriend Day as an excuse to "clean up" your friends list guilt-free. Keep watch on your frenemies.

These days, it seems like the immediate response to being insulted or betrayed is, "OMG I'm going to delete them from Facebook." But don't forget this saying: Keep your friends close, and your enemies closer. If life is a battlefield, then for some, Facebook is the front line.

Take advantage of it. You don't have to interact with your enemies (er, frenemies?), but you can use the News Feed to keep tabs on them. Value their information.

Facebook isn't only about maintaining friendships. Consider other ways in which your potential unfriendees interact with Facebook. Do they post interesting or helpful links?

Are they an expert in a field that's relevant to your work? Remember that most people have something valuable to offer, so consider a person's knowledge, skill set, and connections before unfriending. Consider privacy settings.

If you're inclined to unfriend someone to protect your privacy, there are other ways to hide your information without deleting someone. You can choose to hide your wall, photos, status updates, or other content from just a few people--or entire groups of people. Also very useful is the ability to control specific posts.

Check out this Facebook privacy guide for a clear explanation. Thank you, Facebook. Control your news feed.

Some people are obnoxious status updaters who simply clog your News Feed and put a damper on your Facebook experience with gems like, "I'm so sad. Why do I always get this upset? I forgot to put sugar in my coffee;" or "OMG, I just bought the best stuff ever!

Sure, their behavior may warrant an unfriending, but you have another option: Hide them from your News Feed. Next time they post something like, "Dontcha wish your gurlfriend was hawt like me?" mouse over the update, and an "X" button will appear. Click the X and select "Hide all by _______".

Their posts will no longer appear in your timeline. If you change your mind (or they change their habits), you can undo this setting. Define your "friends."

Set some guidelines, like whether or not you'll add work friends, acquaintances, business contacts, blog readers, and so on. Or maybe you'll only add people you're really friends with. Whatever you decide, stick with it--not only will it help prevent future unfriending, it'll also remind you who you've given permission to view your content.

Don't add them in the first place. Unless it's the rare "friends at first sight," don't send a friend request to someone after meeting them for the first time. It's an obvious I'm-adding-you-because-we-officially-met-and-now-I-can-Facebook-stalk-you move.

You may find that you and this person never meet again, or your "friendship" fizzles due to your premature friend request that forcefully bypassed the real-life steps necessary to build a real friendship. Admit it, you only wanted to look at their photos. The friend-purging status update.

In the spirit of National Unfriend Day, you've decided to delete those unworthy of your profile. Now, sign off Facebook and be satisfied with your actions. Again, don't do it.