I knew this one for quite a few days. I chose the scene where Santana tells off Sue so badly, even Sue gets upset. While I love Sue, I still think after 5 seasons it was about time someone told her off for real. And who other than Ms. Santana Lopez could do that? It was in the Finn Tribute episode. But here's a video, it eplains itself.
To keep it short, it was the most flawless scene in the show.
Day 14- A scene/moment that made you happy