25. "The New Girl" (Season 2, Episode 5)
Most of Season Two gets dragged down in piddly subplots: the Stand-Up Comedian (practically the only character on Mad Men who can't sell a joke), the Comedian's Wife (Don's least seductive seductress by a mile — somebody offer this lady a cough drop), Peggy's friend Father Creepy O'Eyebrows (the silliest one-man anthology of Hollywood Irish-priest cliches since M*A*S*H*'s Father Glasses McBoxing). But "The New Girl" has that stunning scene where Don visits Peggy in the hospital and gives her stern advice: "Get out of here and move forward. This never happened. It will shock you how much it never happened." Their whole strange relationship springs from this moment.
Best line: "I guess when you try to forget something, you have to forget everything."—Don Draper