I had a fairly amusing encounter playing World of Warcraft last night. As I was walking out of the inn, I met a mage who -- without preamble of any sort -- challenged me to a duel. I saw no reason not to accept, and I sicced my wolf on him as soon as he went hostile. A second later he had turned me into a sheep, which kept me out of the action for a few moments. When I became myself again, I couldn't see my adversary anywhere. Shortly after, I discovered that my overeager opponent had fled out of the duel area. Evidently he was no match for my wolf alone, let alone me and the wolf together.
Some other fellow invited me to group with him. I accepted to close the popup window while we discussed it, but he promptly ran off. He evidently expected me to follow him around without even a discussion of what quest he was trying to complete. Rude... very rude, so I dropped out of the group without further adieu.
Point of etiquette, folks. If you're going to invite someone into a group, explain the mission, determine everyone's role in the group, and don't just run off expecting someone five levels higher than you to do whatever you want.