'Game of Thrones'
The Red Wedding (Season Three, Episode Nine: "The Rains of Castamere")
A plot twist so shocking its nickname became a permanent part of the pop-culture lexicon within hours of airing. The wedding-night massacre of Robb, Catelyn, and Talisa Stark by their turncoat followers Walder Frey and Roose Bolton didn't just kill off a trio of main characters — it eliminated the show's central Stark vs. Lannister conflict, driving a dagger into the heart of what we thought the story was about. Series creators David Benioff and Dan Weiss came right out and said this sequence was the reason they wanted to make Game of Thrones in the first place, and it showed.