Tanks who do not understand the abbreviation 'CC'.
Tanks who think they are Rambo and make massive pulls without using a survival cooldown, and blame the healer. (Extra special if they make the Rambo-noise while pulling.)
Warlocks who did not train the spell Banish.
Mages who use Blizzard on single-mob pulls.
Mages who use Blizzard on top of CC'd mobs.
Rogues/Warriors/Deathknights who claim to not have an interrupt.
Any tank not spec'd into their tank tree's respective crit immunity talent. (Extra special if they didn't spend points on it so they could do more dps.)