What tipped me off was Debbie's overcoat.

"It must be fun to write for Captain Holt, knowing that Andre Braugher will kill it when asked to, say, recite the full URL of an article he read online."

I especially loved that they kept this from being another "Don't these people have jobs?" by explaining up-front that everyone was benefiting with a night off, courtesy of Holt and Jake donating overtime. It's the little things that make this "A" well-deserved!