The cast and crew of Mad Men recorded a sing-a-long to the song 'Bye Bye Birdie' from the 60's musical of the same name for showrunner Matthew Weiner.  It's also worth noting in the episode Love Among the Ruins in Season 3, the agency was tasked with repurposing the same song for a jingle for a diet soda for women.  I'll guess the video was recorded at the same time. Personally, I love seeing John Hamm being silly alongside January Jones.

Hit the jump to see the video, and make sure to watch after the song for all the bloopers.  Mad Men returns with new episodes this summer.

Thanks to JustJared for finding the video.

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