Michael Milken donned a cardigan sweater for his “Grease”-themed Rydell High School Sock Hop on Saturday night. Larry Gagosian sported a shirt with convertibles on it, and lots of other guests came as Pink Ladies and T-Birds for the bash at East Hampton Studio to benefit the Prostate Cancer Foundation. David Koch and wife Julia took the dance floor and jammed out to Hall & Oates’ set including “Maneater.” “It was teetering between a sock hop and the moves Elaine did on ‘Seinfeld,’ ” said one onlooker. Newly single Stewart Rahr arrived with a young brunette on his arm and donated $3 million to the foundation. Former governor David Paterson was also there, joking he had hoped to get involved in the tennis game planned for this event. “They didn’t ask me to play tennis. Here’s the thing, I got a mean service, but when they return it, I have no idea when that is.” On his party outfit he said, “I didn’t get the memo. This this is my ’50s preppy outfit. All the preppies that acted like squares — I’m representing them tonight.” Other guests included John Paulson, Steve Schwarzman, Richard and Karen LeFrak and Eddie Trump.