Season 10, episode 24: "Fear (of the Unknown)"
No Grey’s Anatomy season finale is ever calm, so of course this episode features a mall explosion on top of Cristina ruining us with her mushy goodbyes (she's even giving out hugs, for crying out loud). Sandra Oh gives one last hurrah as the edgy, complicated, blunt, always fearless Cristina Yang, who's waiting for one last thing to feel finished before she jet sets to Switzerland. It turns out that that one last thing is dancing it out with Meredith to Tegan and Sara's "Where Does the Good Go." Before leaving for real, Cristina gives Meredith a much-needed talking to about Derek, uttering the infamous lines, "He is not the sun. You are."