The occasion was Kiki de Montparnasse’s evening of “erotic entertainment and discovery” (which began with a dinner at the SoHo skivvies store and then moved East to Chrystie Street), and Ms. Sobieski—blonde, dewy, gratuitously tall, alarmingly unguarded—was dressed as a Latin phrase.

More specifically: “My conceptual bullshit costume is Memento Mori. When you realize your death is inevitable.” She paused. “But it’s not necessarily sad. It can be liberating!”

Memento Mori, which roughly translates to “We’re all going to die,” is also the name of a Streets song (we knew it sounded familiar), an X-Files episode, and a thriller starring Guy Pearce (for which it was shortened to Memento). Ms. Sobieski’s was one of the more intellectual disguises in a low-lit room which also featured an Amy Winehouse, a James Dean, a few priests, a Where’s Waldo, a man wrapped in bubble wrap, an entire zoo’s worth of feathers, Andre Balazs in a fro and cape, and wait—was that a gay Dumbledore?

Ms. Sobieski’s friend, the headgear-happy socialite Arden Wohl, wore her usual flapper dress and headband, all white (Wedding Arden?). Meanwhile, a nubile, buck-naked woman in black-feathered headdress roamed the V.I.P . area in high-heels (when pressed for an explanation, she said she was paid to do this twice a week), and Derek Blasberg holed up with Ashley Olsen (a wise man and a flapper?) in one of the private boxes overlooking the stage. Guests Josh Hartnett, Gemma Ward, Fabiola Beracasa (shark-bitten scuba woman?), Serge Becker, Sante D’Orazio, and Lance Armstrong (whom gossips have associated with the young Ms. Olsen) mingled with the masquerading masses over rock-candy lollipops and blood orange cocktails made with the Brazilian cachaca, Sagatiba, which sponsored the event.

By 2 a.m., the stage featured dancing guests and an excess of pectorals, while the club’s infamous cabaret acts were relegated to an elevated platform in the middle of the room: “Hors d’oeuvre” acts, said one Box staffer, a magician (one such hors d’oeuvre, a midget dressed as Michael Jackson, did the moonwalk on an elevated platform nearby).

Ms. Sobieski, meanwhile, took in the scene, wondering, at one point, what The Daily Transom thought of all this (she herself was here because Mr. Hammerstein was a friend). “I miss trick-or-treating,” she said.