Almost every warlock I encounter tries to put seed of corruption on all four of my toons. Never works. It's kind of a good idea, and would work if they were behind a tree or something and I wasn't paying attention.

Biggest fails are holy nova spam, volley, and hurricane.

Arcane explosion from solo mages. Won't work against my group - two 5 second silences, two death coils, four aoe fears. In group pvp its a bit more effective if I"m fighting others or low on cooldowns, but in general I just wreck stupid mages that try that nonsense. We're not shaman