What story-line would you say had the best build-up, yet had the worst pay-off in the end? I myself would’ve voted for the whole "Who is stalking Undertaker’s wife Sara?" in 2001. After it was revealed to be DDP, the whole thing went down the shitter fast.
Take your pick from 1999, but if anyone can find a more terrible example than the Higher Power than I would have to call them a LIAR.