We've all had times where other players have felt the need to "inform" us of the error of our ways and I'm all for constructive criticism or helpful tips. I am not the best tank/healer/dps and I make my share of mistakes as I learn and adapt to improve my overall gameplay.
But that particular situation just blew me away. I wish that I would have taken some screenshots because my re-telling doesn't do it justice. That poor fellow was just dead-set that I was an idiot and that I didn't belong in that LFR run with him because I didn't have any clue how to gear or play my role.
The nice thing was that after he left I received many /raid and /whispers comments about how I was performing well above my co-tank and that I was doing everything correctly during the boss fights. In fact, a couple of people even commented that the co-tank was using some questionable gear himself and had no place telling me what gear to use.
Anyway, thanks for the interesting thread everyone. I'm generally a lurker and not a poster but I felt like sharing this time. Enjoy the game and have fun!