DINNER AT THE CLUB: “You have to try the corned beef,” said Ralph Lauren to his dinner guests at the new Polo Bar off New York’s Fifth Avenue on Wednesday. “It’s the best corned beef ever.” It was hard not to agree with him — it was that good. So were the New York strip steak and burger, but then again, Lauren has honed the craft at his other eateries in Paris and Chicago. The designer drew an impressive crowd to the first of two private dinners to unveil the new restaurant. The designer, Michael Bloomberg, Henry Kravis and Steve Schwarzman and their respective others were all seated in an alcove that one guest referred to as “billionaire’s row.” (For the people counting, Bloomberg’s billions — $34.6 of them — dwarfed those of the other three.) When Donna Karan arrived with Calvin Klein, the latter gave Lauren a warm embrace; later in the evening, Lauren swung by the other two designers’ corner table, where Klein was eating oysters, and the three icons of American fashion had a long, friendly chat. Other attendees included David Gregory, Hoda Kotb, Tom Brokaw, Brooke Shields, Jonathan and Lizzie Tisch, Allison Williams, Graydon and Anna Carter, Glenda Bailey and Linda Wells, as well as most of the Lauren clan, including Ricky, Andrew, David and Lauren Bush Lauren, as well as brother Jerry.