Spoiler alert! We're discussing surprise actor cameos in the Netflix movie "Unfrosted" (streaming now), so beware if you haven't seen it yet.

Directing and starring in the new Netflix comedy “Unfrosted,” Jerry Seinfeld revisits some of his favorite things (cereal, Pop-Tarts, NASA and the 1960s) with some of his favorite people.

A slew of actors and fellow comedians are sprinkled throughout the outrageous, semi-true origin story of Pop-Tarts, from Cedric the Entertainer, Bill Burr and Dan Levy to Amy Schumer, Peter Dinklage and Hugh Grant, plus “Saturday Night Live” alums like Fred Armisen and Bobby Moynihan. The best cameos, however, come in Seinfeld’s unexpected – and downright hilarious – “Mad Men” reunion.

Seinfeld tells USA TODAY that he’s “a gigantic fan” of the Emmy-winning drama (which aired on AMC from 2007 to 2015) and is “friendly” with the show’s stars Jon Hamm and John Slattery, who reprise their respective roles as Don Draper and Roger Sterling in “Unfrosted.”

In the movie, Kellogg’s employees Bob Cabana (Seinfeld) and Donna Stankowski (Melissa McCarthy) are ready to mass-market their toaster pastry, but they need a snazzy name to sell it. Head honcho Edsel Kellogg III (Jim Gaffigan) calls in two “can’t-miss Madison Avenue ad men” to help.

Enter Jon and Roger, who pitch the idea for “Jelle Jolie” as the name with art of a wife in a negligee holding an oversized Pop-Tart – which is a little sexier than the Kellogg’s folks are expecting. “I’ve been in your town for six hours, you know what I see? Dead trees and sad lonely women,” Roger quips, while Don gives them a choice: “Raisin Bran and irrelevant, or provocative and revolutionary.”

Edsel wants more time to think about it and the ad men get, well, mad. “I’ll be retired on a bluff overlooking Stinson Beach while you’re still genuflecting before the god of mediocrity,” Don says in his flurry of barbs aimed at Bob, though he takes the time to flirt with McCarthy's Stan before leaving. (The two “Mad Men” characters are also seen in a later scene after the Pop-Tart finally gets its official name. “That’s gonna sell,” Roger says as Don rips up the Jelle Jolie mockup back in their New York office.)

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Seinfeld had the idea to bring the “Mad Men” personalities into his movie's narrative because he figured they’d be around then. (“Unfrosted” is set in 1963, which falls within the show’s timeline.)

“Maybe these Michigan guys were thinking, ‘Hey, why don't we get some slick New York guys in here to help us with this?’ And our favorite thing of ‘Mad Men’ was how hostile the agency would be to the potential clients,” Seinfeld says. “Like, 'If you don't like this idea, you're an idiot.' Insult them in the meetings. We just thought that was so funny.

“We wanted to re-create that hostility: 'You'll never swim the English Channel and drown in champagne.' All these kind of lyrical putdowns. ‘Mad Men’ is just the best. So that was a dream come true to be in a scene with those guys. To travel to that time and place for me was fantastic.”