/firmhandshake

Cruising around the internets, I ran across Killed in a Smiling Accident's Guide to MMO Etiquette, Chapter 1, which made me laugh more than a little:

Seeing a stranger (enemy faction in a PvP game)

You may attack them, but you should wait for them to despatch any mob they are fighting first[...] If they are climbing a cliff, you should lower a rope, and offer them a chance to rest before engaging in combat, after checking whether they have six fingers on one hand.

The whole thing is definitely worth a read.