Glutton for Fiery Punishment

In Archmage Xylem's Trial of Fire in Azshara, gain 10 stacks of Fire Dancing without taking damage.

This can most easily be accomplished by simply following Darwin the blood elf apprentice. He will dance, but you don't have to in order to gain the 'Fire Dancing' buff. There is a quest chain involving the trials, but it is not necessary to do the quests in order to gain the achievement.