When is it rude to @ someone on Twitter?

It's hard to imagine this today, but when Twitter was launched on March 21, 2006, it wasn't intended to be used for conversation. Say what?! Yep, its initial purpose was for status updates or brief, important messages. For example, "At Starbucks on Main." Or, "Accident on 5th + Lacy. Use Bristol exit." Founders did not incorporate any means of replying to someone's tweet, or retweeting someone's message. But it didn't take long before users of the nascent social media began adapting it to their needs and desires. One of these was, yes, being able to reply to someone's tweet. Another was to be able to catch a particular person's attention so they'd read your tweet -- sort of like being able to shout, "Hey John! Listen to this!" The way both problems were solved was through use of the @ symbol [source: Seward].

The first person to use the @ symbol in a tweet specifically to call out to another user (as opposed to the common practice of using it as a substitute for the word "at") is believed to be one Robert Andersen, who tweeted pal Buzz Anderson on Nov. 2, 2006, "@ buzz - you broke your thumb and youre still twittering? That's some serious devotion." Presumably, Buzz noticed the tweet.

The staff at Twitter certainly did. Six months later, on May 30, 2007, Twitter unveiled "@ replies" as an official feature. Rules then stipulated there could be no space in between the @ symbol and the person's name if you were trying to reply, plus the tweet had to start off with "@buzz" (or whoever you were responding to). So Andersen's usage -- he started with the @ symbol and buzz's name, but inserted a space in between them -- was incorrect in retrospect. The first accurate @ reply tweet was done by developer Neil Crosby on Nov. 23, 2006 [source: Seward]. Don't tell that to Andersen, though; if you go to his Twitter account home page, @rsa, his bio includes the lines, "Accidental sender of the first Twitter @-reply. Sorry."

While Twitter made the @ symbol an official way to answer someone's tweet, use of the symbol with someone's name within the tweet -- not just at the beginning -- was also a way to call out to that person.

A fair number of people don't understand exactly how the @ sign works in a Twitter conversation. You can use it in the standard fashion; that is, as a substitute for the word "at." But its true value lies in its use as a way to respond to people, mention them or start a conversation. Let's say your acquaintance Josh (@JoshBuhr on Twitter) tweeted that he just ran 2 miles. To respond, you can now simply hover your cursor over his tweet and click on "reply," which is the single arrow on the bottom left of the tweet box. When you do that, a box will pop up with "reply to @JoshBuhr" already written in it. You type the rest. For example: "reply to @JoshBuhr you wimp! I just ran five." You could also simply tweet, "Hey, @JoshBuhr, you wimp! I just ran five." This is called a "mention." If you send either of these tweets:

But what if you don't want the entire Twittersphere (and universe) to be able to read that tweet to Josh? When you opened your account, you were asked whether you wanted to keep your tweets public (the default setting) or private. Most people select public. If you change this setting to private, no one will be able to view your account and its tweets unless you manually approve them[sources: Twitter, Twitter]. You can also elect to send Josh a private, direct message by clicking on your messages tab.

Because people don't always understand every nuance to Twitter, misuses of the @ sign can occur. For example, let's say you wanted to make a snarky tweet to your followers about your soccer coach, Bill Bong -- like whispering about him behind his back. So you tweet, "@BillBong is such an idiot coach! Hate him!" But because you put "@BillBong" in your tweet, it will go into his notifications and mentions tabs. And if Coach Bill is following you? It will also show up in his home timeline. Oops. And, as mentioned, it will be on your profile page.

You can delete a tweet you didn't mean to send, but if others have already retweeted it or quoted it with a comment of their own, the tweet will remain part of their message.

Of course, sometimes people purposely "@" someone on Twitter because they're angry or just plain mean. Or they simply don't care if the person they're slamming finds out. That's not cool. But unfortunately, that's life. Now that know how to properly use the @ symbol, make sure to use it wisely.