When I am about to kill some one for a quest, and someone comes running to kill him, I would rather get an invite to join the group (even without a whisper) than get ninja'ed, but that seems to be the primary exception.

Regarding getting invited in the LFG channel, I auto-ignore anyone who invites me without talking to me before. I just find it's easier because I usually put myself in LFG for multiple things at the same time and I never know what I'm getting invited for.

Or the people that invite you (with me being a priest) with your LFG note saying "SPRIEST!!!!!!!!!!!!" and say, "you're holy, right?"

Read the LFG text!!!!!!!!

I've always been amazed at how people will randomly invite me to groups without so much as a tell. In my previous MMO this was customary, you never invited someone without an explanation- that would be just plain weird.

Especially when the person isn't even in eye shot. Actually, I've had this one guy that's been randomly inviting me since level 22, over a month ago... despite that my druid is now 70 and he is still 20 or 30-something.