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As ubiquitous as alcohol and tobacco in the Mad Men universe. Leading the pack of strayers is Don, who stepped out on his wife, Betty (January Jones), with at least four mistresses, including Bobbie Barrett (Melinda McGraw, above). Unapologetic rogue Roger Sterling left his wife for Don's secretary, while Pete Campbell, Harry Crane (Rich Sommer), and even lily-white Betty have all had extramarital flings of their own.
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Pointy as a Cuban missile, these undergarments provide the women of Mad Men with their distinctive silhouettes. They were also the centerpiece of Sterling Cooper's Playtex campaign, built around Paul Kinsey's (Michael Gladis) theory that all women are either Marilyn Monroe or Jackie Kennedy. This season, Don asked his hooker not to take off her brassiere in bed.
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C: ''C'EST MAGNIFIQUE''
At a dinner party with her rapist/husband's colleagues, Joan awkwardly sang this 1953 Cole Porter love song while playing the accordion. A snapshot of the misery of Joan's marriage.
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D: DOG TAGS
Don's ticket to escaping his past. During the Korean War, the man we know as Don, but whose real name is Dick Whitman, stole the dog tags of a slain soldier named...Donald Draper. Dick assumed the dead man's name and started a new life for himself. Soon after Betty discovered the secret, she asked for a divorce.
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E: EUGENE SCOTT ''GENE'' DRAPER
Named (against Don's wishes) for Betty's difficult father, baby Eugene is the youngest of the three Draper kids — and seemingly Betty's favorite, especially since he doesn't sass back like his sister, Sally (Kiernan Shipka).
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F: FAINTING COUCH
Betty irritated her interior decorator by impulsively buying one of these Victorian-era loungers.
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G: GREENWICH VILLAGE
The bohemian NYC hood where Don visited his first-season mistress Midge (Rosemarie DeWitt). Post-divorce, he now lives there.
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H: HENRY FRANCIS
Betty's second husband (Christopher Stanley) seemed like a white knight when he romanced her in season 3. But the couple have settled into an uneasy married life — aggravated by Henry's shrewish mother.
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I: ''I HAVE A DREAM''
Don listened to Martin Luther King's speech at the beginning of season 3's ''Wee Small Hours,'' and Carla (Deborah Lacey) was absorbed by King's ''Eulogy for the Martyred Children'' at its close.
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J: JOHN AND MARSHA
Peggy and her copywriting partner, Joey (Matt Long), jokingly performed this 1951 comedy routine. A hit recording from humorist Stan Freberg, the bit spoofs soap operas, portraying an amorous couple whose only dialogue is each other's names.
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K: KODAK CAROUSEL
The best of Don's grandiloquent monologues was his pitch for the new slide wheel.
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L: LAWN MOWER
In season 3, the series demonstrated the formula for eliminating an annoying new boss: Drunk secretary + John Deere = severed foot. You're guaranteed he'll never return to the office.
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M: MENKEN'S DEPARTMENT STORE A Fifth Avenue emporium headed by the shrewd, sexy Rachel (Maggie Siff). Don took an interest in Rachel's intimate apparel, and the two embarked on a steamy affair. He extended her the rare invitation to run away with him — and she issued the rare refusal of Don Draper.
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N: NIXON-KENNEDY PRESIDENTIAL ELECTION
Sterling Cooper staffers threw an election-night party (complete with a watercooler full of créme de menthe). But the real action of the episode came when Pete revealed Don's secret ''Dick Whitman'' past. ''Who cares?'' asked Bert Cooper (Robert Morse). In fact, we all did.
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O: OSSINING, N.Y.
Where Betty and Don made their unhappy home, now the source of divorce-settlement tension.
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Though Peggy went on the pill in the series premiere, in that same episode she got pregnant by Pete. But she didn't realize she was pregnant until giving birth to a boy, whom she put up for adoption. A year later, at the end of season 2, Betty discovered she was carrying Don's third child. She contemplated abortion but eventually carried baby Eugene to term.
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When young Euro Kurt (Edin Gali) nonchalantly came out to his colleagues in season 2, Ken Cosgrove (Aaron Staton) muttered, ''I knew queers existed. I just don't want to work with them.'' The exchange was torture for the closeted, married art director Sal Romano (Bryan Batt, above left), who eventually lost his job for rejecting the advances of a male Lucky Strike executive.
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Peggy's clever campaign for this vibrating belt for ladies helped get her promoted.
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S: ''SHUT THE DOOR. HAVE A SEAT''
The name of the game-changing third-season finale, in which Don, Roger, and Bert — facing a takeover by rival McCann Erickson — got themselves fired to form their own agency with onetime British nemesis Lane Pryce (Jared Harris), Pete, Harry, Joan, and an initially resistant Peggy.
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T: TRUDY CAMPBELL
Pete's long-suffering wife (Alison Brie) comes with overbearing parents (make that rich overbearing parents). She wants a baby, and is saddened that she and Pete can't conceive. Little does she know there's living proof that Pete is plenty fertile.
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U: UTZ POTATO CHIPS
Motormouth comic Jimmy Barrett (Patrick Fischler) was Sterling Cooper's choice as the spokesman for the snack-food brand. Jimmy's wife, Bobbie, was Don's choice...for other things.
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Don vindictively plied Roger with oysters and martinis so he'd upchuck in front of important clients.
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W: WHO IS DON DRAPER? The question that a reporter for Ad Age asked at the start of season 4.
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X: XEROX MACHINE The first fully automated plain-paper copier, and a cause for great jubilation among the secretaries.
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Y: ''YOU DON'T KISS BOYS. BOYS KISS YOU.''
Betty's attempt to teach Sally the same rigid gender roles that define her own cloistered existence. Betty's not gonna like seeing Sally burn her bra.
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Freddy Rumsen (Joel Murray) played Mozart's Eine Kleine Nachtmusik by zipping and unzipping his fly. You're welcome, ladies!