Working as intended
The content of this article is not part of official Warcraft lore, but has nevertheless become part of the World of Warcraft culture or community.
Famous Game Master Quote
More often than not, the feature truly is working as intended, but many recent bugs have been declared "Working as Intended", while they actually WERE bugged. For example the infamous change to 
[Frost Trap] in release 2.0.1 (which makes no sense in a real-life context) where the effect continues even after the player has left the trap's AOE, have made players weary of the GM response. "Working as Intended" is commonly used when players complain to each other about such bugs, and a number of servers even have guilds named "Working as Intended", mocking the response.
How many GMs does it take to change a lightbulb? - None, it's working as intended!
Imbalance
"Working as Intended" is often used in a similar vein to reply to complaints of imbalance, unfairness and other perceived injustices. Frost mages critting for 2 million damage with 
[Ice Lance]? Working as intended! 25-day cooldown on 
[Judgment]? Working as intended! Blood death knights outlasting a dozen opponents while using Vengeance to deal more damage than all their attackers combined? Working as intended! This may be used to express the opinion that Blizzard are intentionally and maliciously creating the problem, that they have no plans to fix it, or simply to express delight, confusion or apathy with regard to the current state of affairs.