A ton of people have been linking to this, which is meet and right, because it’s excellent. (There were even a couple of things I, Past Master of Tweets, didn’t know.) However, I need to make a few small edits:
• Due to the nature of Twitter, it’s common for a tweet to end up on many people’s timelines simultaneously and attract many similar replies within a short span of time. It’s polite to check the existing replies to a popular tweet, or a tweet from a popular person, before giving your two cents.
After “polite,” add “but almost unheard-of.”
• It’s generally considered rude to barge into the middle of a conversation between two other people, especially if they seem to know each other much better than you know them, and especially if you’re being antagonistic. There are myriad cases where this may be more or less appropriate, and no hard and fast rules. You’re a passerby overhearing two people talking on the street; act accordingly.
In the first sentence of that quote, delete “It’s generally considered.” Such behavior is of course rude, but nothing on Twitter is “generally considered” rude. Alas.
One other etiquette matter I would mention: some people have figured out that I have a locked account and tweet at it, hoping I will notice and (I guess) respond. To me, this is the equivalent of walking up to a hotel-room door that says “DO NOT DISTURB” and pounding on it. This annoyance could easily be eliminated if Twitter had a setting for not showing me @-messages from anyone I don’t follow* — a setting that surely many people who suffer actual harassment on Twitter would want to take advantage of, at least at times, and which ought to be the default for locked accounts. Locked accounts aren’t very private if you regularly have to deal with noise from strangers.
* My bad, Twitter-for-web does have that setting — it’s just, I believe, not part of the API and therefore not available to any Twitter clients, including Tweetdeck. But I have found that even if I use Twitter-on-web, which I never want to do because of its annoying eccentricities, that choice is not sticky: I set the tab to “show replies only from people you follow,” and if I leave that tab and return to it the setting has gone back to “show replies from everyone.” Thanks to Gabriel Rossman for reminding me of the setting on the home page.