It would have to be the scene that marks the middle of the “real” conversation between Jeff and Abed, when Jeff starts arguing with Abed, the scene in which he brings up the ants and what-not.  To me, it’s like watching two F-15s roll and switch places mid-flight.  By arguing that there is no such thing, Jeff initiates possibly the first real conversation of his life, and, thanks to the spectacular talent of Danny Pudi, we get to watch fake “real Abed” gradually slip back into “real” real Abed.  Danny, at the top of that scene, is five percent Abed, then fifty percent in the middle, then ninety five at the end.  It’s incredible to watch, for me, anyway, and all credit for that goes to the director and actors.  Thank you Richard Ayoade, Joel McHale and Danny Pudi for making the most anxiety-ridden experiment of season two into one of which I can proud for the rest of my life.