I know I have mentioned muting (also called Blocking, in many viewers) here several times in passing. But let's talk about that more specifically today.
There is no true privacy in Second Life, unless you are rich and buy your own isolated region. That means we have to deal with other people all the time...and some of those people are, to put it mildly, jerks. What can you do about a rude and annoying person, especially one who seems to be stalking you and showing up everywhere you do? What about that idiot in your favorite club who's always throwing huge chat spam gestures out, or yelling HOOOOO?
Block them, that's what. Right click their avatar and choose Block (or Mute) from the context menu. Suddenly they become invisible, except for their nametag. Or, depending on your viewer and how you have set your Preferences, they might be a green cloud, or a gray silhouette.
People on your Block list can't be heard in local chat, voice, or IM. Anything they send you will be automatically refused. They have become, as far as you are concerned, a non-person.
If they aren't physically present, you can Block someone with a button in their Profile, if you use Firestorm or another viewer that has that feature. The official LL viewer does not, but you can click on a person's name in an IM history window and Block them from there. (This is a very annoying omission on LL's part. You can Block someone in your Friends list, but unless they are right there with you, you have to jump through hoops to block a stranger. I hope bringing the Block button back to the profile is on LL's To Do List.)
There IS one way in which a blocked avatar can still interact with you: they can hit you with physical objects. So you may need to be a little fast on your feet if the blocked jerk jumps in his car and tries to run you down, or starts hosing you with an AK-47.
If you send someone an IM, pay them money, or send them an item, they will be automatically unblocked. Unless of course, they have blocked you, too! But there is also a Block list in the People window, and you can unblock someone from there.
You can Block objects too. Things that send out annoying sounds or repeated group invitations are good candidates for this. Muting an object will also mute its owner, though.
Sometimes you will get a Block option through a menu. For example, many popular dance machines in clubs will have a little Block button as a menu choice. Be careful you don't hit this by mistake! If you do, you will wonder why the dance machine isn't working any more, until you figure it out and unblock it from your list. if you want to close the offered menu, use the Ignore button instead.
Blocking someone is truly a way to get the last word. Just say to them, "You're muted, jerk," and hit the Block button. You can then grin evilly to yourself as you watch their silent presence and think about how frustrated they must be that they can't annoy you any more.
See the official word on Blocking here: