I remember reading this once. It was a Supernatural/Vampire Diaries crossover in which one of the SPN brothers wants to go to Mystic Falls to hunt some vampires/investigate abnormal activity, but the other brother tells him that they can't because Mystic Falls has something very dangerous, known as Plot Advancement, and stuff will actually have to happen on a regular basis.

If anyone can link me back to this, I would be eternally grateful.