Prerequisite quest - Mark of Quality.
Upon completion of that quest, you will receive the second part in the chain, Quality. The yetis you must kill for that quest will randomly drop a Perfect Yeti Hide. You must have completed The Mark of Quality to see and loot the hide. Some yetis in north Feralas will seem "bugged" and cannot be skinned if you have not yet completed the quest.
This quest is repeatable, but the hide itself is unique.
The Alliance have an identical quest, Pristine Yeti Hide