Everyone's whooping it up in the conference room, but before Don can trudge his way in there, Peggy appears with congratulations. And of course he's upset about Joan, but the fact that even now he can treat her like something he just scraped off his shoe really drives home the idea that she's doing the right thing here. Peggy thinks their conversation can wait, but Don's not in the mood for celebration prompting her to observe, "You really have no idea when things are good, do you?" I'm not sure I'd agree with that, but now is SO not the time, as Peggy -- already starting to sniffle a bit -- leads the way into his office. He asks her to drink with him, which signals to me that he's looking for some emotional solace, so this is obviously going to be even more of a blow than you'd normally expect. She tells him she has to discuss something serious and he tries to be conciliatory, but given that he babbles about how (a) he can't put a girl on Jaguar and (b) Joan just got made partner, he's not helping his case. Whether because of this news or not, Peggy steels herself with a long sip from her drink before stepping forward and telling Don that the day he saw something in her, her whole life changed and since then, it's been her privilege that he treated her like a protégé. Don leans back in his chair with a wry grin like he knows how to handle this, but the way the color drained from his face during the speech was the telling moment. When she concludes that she needs a new experience and has accepted another offer, he, with AMAZING fake amused condescension -- one second he looks like he's actually smiling and another his mouth looks like a dead clown rictus -- asks if she's done, but when she plows on about her notice and last day, he heaves an ersatz sigh and tries to tell her he knows it's been crazy and she's been feeling unappreciated and what's more, he's impressed: "You finally picked the right moment to ask for a raise." Don, you're missing the point; she doesn't want money and even if she did, she'd probably be afraid you'd pelt her in the face with it.