When my guild use to have Teamspeak, we would always plan out our strategy before taking on a particular tough mob or boss.
In the Leeroy Jenkins movie, the raid group was at the part in the UBRS dungeon where a bunch of Dragon Whelping eggs are scatter all over a room. If you got too close to the eggs, they would hatch and spawn whelpings. In WoW, trying to take on more than 10 mobs in a raid group of 15 can be tough if the tank isn't able to hold aggro and if the mages in the group aren't able to AoE the crap out of them without causing too much hate. The problem with Leeroy obviously is that he ran in there like a dork, waking up all the dragons all swarming the whole raid group with like over a dozen whelpings. I'm assuming Leeroy was their tank (Leeroy is a dwarf warrior and I don't recall seeing any other warriors in their group) and he obviously wasn't trying to tank them. The whole party panic'd and no one dared try to fight them as a group so they all died. Stupid Leeroy, lol.
BTW, I do realize that the Leeroy film was staged but what they were doing isn't exactly uncommon. Some of the worst PUGs I have ever been in are actually dumb like that! Guild raids are usually always better than PUGs.
Dictionary (In case I'm using terms no one understands):
Tank: The player who's job is to get the enemy to focus on him so they don't attack the weaker players. Warriors are usually the class that does this.
PUGs: Pick up group. A bunch of players that usually don't know one another or aren't all in the same guild.
Aggro: The aggressiveness / hate level of a monster. The more aggro a player has towards a certain monster, the more likely the monster will attack them.
Mob: Another name for an enemy NPC or monster.
AoE: Area of effect. Spells that can effect more than one monster within a certain radius.
The cake is a lie... THE CAKE IS A LIE!!!!!