"It's just epic," spake Larry Gagosian. And it was so. The gallery titan was referring to client Jeff Koons' Split-Rocker, a mammoth floral sculpture lately debuted at Rockefeller Center. Part Pop Art, part playground, the artwork stands nearly 40 feet tall, covered in more than 50,000 flowers for an effect that's both wondrous and faintly terrifying. An art-establishment-heavy cadre including Richard Prince, Jeffrey Deitch, Bill Cunningham, Leelee Sobieski, Brice Marden, Whitney director Adam Weinberg, and Gloria von Thurn und Taxis turned out this afternoon to The Sea Grill to fete the work. Split-Rocker's unveiling coincides with the massive Koons retrospective bowing this week at the Whitney (the last exhibition ever at its soon-to-shutter Madison Avenue location), whose opening reception last night had a heavyweight guest list of its own: Cindy Sherman, Alek Wek, Arianna Huffington, John Currin, and Rachel Feinstein all raised a glass or two. At least a couple of younger members of the Koons clan were spotted racing between tables at lunch, as just a few feet away on the patio, Gagosian admired the installation amid friends, offering up his take on the populist piece. "I think Jeff's work kind of straddles two things: It's very sophisticated, extremely well-executed, but it also has universal appeal. If you know a lot about his work and the history of sculpture, you can understand how it fits in there, and if you're just somebody passing by, you've gotta smile when you look at it."