I have two stories, well really far more than that on the bad side, but one of the two is a good one. This thread is full of bad, so I'll just share my good.
It was still WotLK, and I was a DK dps who queue'd with a healer. The gear inflation let me tank everything in the instance without worry as long as I had my trusty guild pocket healer, so generally I pretended WotLK heroics were 4dps and one healer. One time the tank was yelling at me to let him keep threat on stuff, but considering I was the LoLAoE unholy he never stood a chance. I politely told him, "It's no worry, x healer can heal me through this just fine and it will just go faster until you get a little more geared." The gear comment was just to make the tanks ego a little better, but he quieted down and the run went smoothly.
The real meat of the story was the other DK dps who asked me if he could have a moment of my time, I said sure and he started a stream of questions about how to play a DK. I asked him if he had vent, he replied with "What's vent?" Walked him through the setup, and he sat there for a good 45 minutes listening to me on vent and actually writing down notes. He hung around on vent while he attempted to practice the new information on a test dummy and said he had nearly doubled his dps. He also paid enough attention about strangulate/deathgrip on ranged mobs to pull them into the AoE cluster...it was a pretty refreshing experience from a time I asked a paladin if he could please use "Judgements" and got a reply with several obscenities to have a player actually ask politely, listen well and apply what was learned. It ALMOST restored my hope for this community...almost.