There's a reason why the Parks and Recreation gang is so sad in this scene: Ann and Chris have left for Michigan.
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Leslie throws Chris and Ann a party on their last night in Pawnee on Parks and Recreation. "Chris and Ann" is the 13th episode of the show's sixth season.
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Parks and Recreation Season 6 Episode 13 Quotes

There has never been a sadness not cured by breakfast food.

Ron

I told him One Headlight by the Wallflowers isn’t dancing material and he told me, “Not with that attitude!”

Ann