I’ve now watched “Lost Horizon,” the latest Mad Men episode, twice, and I can’t get this iconic image of Peggy Olson (Elizabeth Moss) out of my head. This plus the drunken roller-skating moment with Roger Sterling (John Slattery), I mean. Even if nothing else happens in Peggy’s life between now and the last episode, it’ll be okay. A dangling lit cigarette hasn’t seemed this sexy or cool since the noir heyday of Robert Mitchum.