funniest has to be back in the 2.1/2.2 patch days. i volunteered to sit out on a raid (since i was geared) and there was a mage in the group who did better dps and knew the fights better than i did, so he was supposed to be the one calling out the strats. Problem was he kept thinking that because he was SSC geared and we were "only in kara" he could do whatever he wanted with no consequence since he outgeared the place. Well, our feral druid MT didn't outgear it and had problems getting aggro back from the mage.
They started the run and an hour later they had downed attumen. The mage kept yelling "I'M LEET, BITCHES" macro'd as he clicked some spells to start the fight (echoing it in our Vent). He caused the wipes because healers got more aggro than the tanks because they were all trying to heal the mage, so when he died the healers died next.
Eventually they kicked the mage and sent me an invite, so to break the tension and make it a "fun" run again, as soon as I walked into the place i charged to the dance hall and pulled a group of mobs, popped evasion and yelled in vent "I'M LEET, BITCHES!!" as the entire room wiped the raid.
Everybody laughed, we came back and finished clearing what we had on farm (up to 'Spite at that time) without any more issues.