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Constance Zimmer as "Waitress #2": Season 9, episode 15, "The Wizard"
Blink and you'll miss the former Entourage and House of Cards star as the waitress who asks Elaine's boyfriend—whom she thinks is black—how he takes his coffee. The choice gives Elaine no further clues.
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Jeremy Piven as "Michael Barth (George)": Season 4, episode 23, "The Pilot"
Everyone liked Michael Barth's tryout for the role of George at the Jerry audition—except George. Piven played Barth, who played the show-inside-the-show version of George, who was played by Jason Alexander. Got it? Got it.
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James Spader as "Jason 'Stanky' Hanky": Season 9, episode 9, "The Apology"
Before The Blacklist, Spader worked through a 12-step recovery program on Seinfeld but neglected to place George on the docket to make amends. George may or may not have induced a Stanky relapse spurred by some rum raisin ice cream.
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Lauren Graham as "Valerie": Season 8, episode 20, "The Millennium"
Before Lorelai Gilmore came into our lives, Graham played one of Jerry's many, many girlfriends. Due to some stepmother hijinks, Jerry ends up in one of Valerie's emergency speed-dial slot and Jerry—not poison control—gets the call when Valerie gets sick. Jerry is amused. Valerie isn't.
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Courteney Cox as "Meryl": Season 5, episode 17, "The Wife"
Meryl pretends to be Mrs. Seinfeld in order to get a dry cleaning discount. What a Monica move.
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Denise Richards as "Molly": Season 4, episode 16, "The Shoes"
Molly is the teenage daughter of an NBC executive that Jerry and George are pitching to. She enters the apartment and takes off her jacket. Jerry briefly checks her out, while George, in an impressively consistent Costanza act, stares and gets caught.
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Cary Elwes as "David": Season 7, episode 21, "The Wait Out"
George breaks up David and his wife after a flippant, joking comment. Apparently it wasn't true love. Thanks, George.
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Mariska Hargitay as "Melissa": Season 4, episode 23, "The Pilot"
Melissa tries out for the "Elaine" role of Jerry and George's TV pilot and enters the scene tactlessly insulting George. She would have been a great Elaine.
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Jon Favreau as "Eric the Clown": Season 5, episode 19, "The Fire"
A Swingers-era Favreau was a clown and the subject of ridicule for his name choice. "Eric?," George laughs. "What kind of name is that for a clown!"
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Christine Taylor as "Ellen": Season 8, episode 14, "The Van Buren Boys"
Jerry is worried that Ellen is lame because she might not have a social life outside of their relationship. Clearly his loss for calling it off.
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Anna Gunn as "Amy": Season 5, episode 3, "The Glasses"
Bryan Cranston's run on Seinfeld as Tim Whatley resurfaced after he laid a smooch on Julia Louis-Dreyfus during last year's Emmys. But his Breaking Bad spouse was also on the show. George thought Amy—Jerry's woman du jour—kissed a horse-faced man, but due to poor vision, it was only a cop nuzzling her actual horse.
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Amanda Peet as "Lanette" in season 8, episode 22, "The Summer of George"
Lanette's big problem for Jerry? The Togetherness and 2012 star happens to live with a guy. Even after she adjusts her life for Jerry, her life proves too exhausting for the man. It's always something with him.
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Debra Messing as "Beth": Season 8, episode 19, "The Yada Yada"
Beth and Arnie (Stephen Caffrey) want to adopt, so they ask Elaine to be a reference. Elaine botches that (naturally), leading to their breakup. Jerry then has Beth accompany her to Mickey's wedding, where there's an unpleasant run-in with dentist Tim Whatley (Bryan Cranston). Jerry expresses his distaste for those in the dental professional, which Beth echoes... before revealing she's a racist. Yikes.
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Jennifer Coolidge as "Jodi": Season 5, episode 9, "The Masseuse"
Jerry's girlfriend Jodi doesn't really want to give Jerry a massage off the clock. Can you blame Stifler's mom, though? That's her day job! Their relationship is thusly short-lived.
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Sarah Silverman as "Emily": Season 8, episode 12, "The Money"
One of Kramer's few on-screen romantic flings. But there's an issue: She moves too much in her sleep. "You're not easy, Kramer," she tells him at Monk's.
"I know," he replies, in a way that's not nearly as sexy or cool as when Han Solo said it.
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Drake Bell as "Kenny": Season 9, episode 18, "The Frogger"
The singer and former Nickelodeon child star was just a kid in a pizza shop enjoying some leisure time on the sticks. Totally minding his own business. But George, in a way only he can, gives over-the-shoulder advice and blows Kenny's spot, only for him to retreat to The Amanda Show. Uncool.
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Molly Shannon as "Sam": Season 8, episode 22, "The Summer of George"
Sam doesn't move her arms when she runs, like fellow guest star Raquel Welch. Don't worry—we know she's at least capable of moving them, even to do something really, really weird.
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Bob Odenkirk as "Ben": Season 8, episode 9, "The Abstinence"
What if Odenkirk got typecast on Seinfeld as a schlub trying to become a doctor, but then ultimately went dirty and resorted to a life of working side-by-side with drug kingpins?
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Janeane Garofalo as "Jeannie": Season 8, episode 1, "The Foundation"
Jeannie is the perfect for woman for Jerry because she's a female Jerry. But they can't stand each other—and then mutually break up without any hard feelings. What an inspiration for us all.
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Jane Leeves as "Marla": Season 4, episode 10, "The Virgin"
Oh, Marla. So naïve. So innocent. It only makes sense you fell for John F. Kennedy Jr. (and then moved to Seattle to help out the Crane family as Daphne on Frasier).
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Patton Oswalt as "Clerk" in season 6, episode 5, "The Couch"
Oswalt hassles George from behind a video-store counter; he can't allow anyone to see who rents what. Let the renter watch Breakfast at Tiffany's and (maybe) Rochelle, Rochelle in peace.
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Mark Boone Junior as "OTB Patron" in season 3, episode 13, "The Subway"
The man who would be Bobby Elvis in Sons of Anarchy explained to an incredulous Kramer that the racehorse Pappanick's parents were both, indeed, mudders. The lecture led to a big cash-out at the betting office for both men.
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Michael Chiklis as "Steve Pocatello": Season 3, episode 10, "The Stranded"
Really hospitable move by Steve, who invited a call girl to Jerry's apartment. But it was probably an elaborate sting by Vic Mackey to bust a poor john.
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Daniel Dae Kim as "Student #1": Season 9, episode 16, "The Burning"
The Hawaii Five-0 and Lost star had an up-close view of Kramer's acting stylings as Kramer mimicked what it's like to have gonorrhea.
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Chris Parnell as "NBC Executive": Season 9, episode 1, "The Butter Shave"
Stu Crespi is one of the two NBC execs who prefer Bania's stand-up set to Jerry's—what is wrong in the world? He only pops up at the end, but it's a glimpse of the type of straight man that would define Parnell's future SNL stint.
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Kevin Dunn as "Joel": Season 1, episode 4, "Male Unbonding"
Maybe Veep's Ben got jaded and hard after Jerry decided to end their friendship. In "Male Unbonding," Jerry accuses Joel of being self-involved; the irony's strong, but he's somehow right.
CORRECTION: An earlier version of this gallery stated Peter Dinklage appeared in Seinfeld via an uncredited voiceover.