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Best: Sally catches Don with his pants down
Episode: "Favors" (611)
A moment as horrifying as any we've seen on "Mad Men" was also one of the year's most unforgettable twists. After Don tells Sylvia Rosen he's found a way to keep her son, Mitchell, out of Vietnam, she rekindles their affair. Unfortunately Sally's friend secretly slipped a love letter under Mitchell's door, and when Sally goes to retrieve it she winds up seeing her father and Mrs. Rosen in a seriously compromising position. Sally is traumatized, Don is humiliated, and the audience is riveted by how far Don has fallen.