The last curtain had fallen. The company had taken its final bow. And the party portion of the American Ballet Theatre's Monday-night Spring Gala was in full swing (cue guests like Zani Gugelmann, Tory Burch, Marina Rust Connor, and Helen Lee Schifter mingling among the dancers and complaining about the unseasonably cold weather). But Olivier Theyskens still couldn't stop talking about That Dress. No, not the chic little sheath on the designer's perennial date Lauren Santo Domingo, but the voluminous white gown worn by dancer Irina Dvorovenko in the piece Splendid Isolation III. "When the lights came up and I saw her there, I think I stopped breathing," exclaimed Theyskens. "Are you talking about the dress?" asked Proenza Schouler designer Lazaro Hernandez. "That was, like, the most amazing thing I've ever seen. Who made it?" Elena Comendador, the dancer and costume designer, for the record. But Dvorovenko's wasn't the only frock that caused a commotion. A shock-horror moment arose early on when mega-social Muffie Potter Aston showed up in the same white Carolina Herrera gown as pal Karen LeFrak. But instead of avoiding each other like the plague, they later joined forces on the dance floor like a pair of sparkly Doric columns.