Billionaire Warren Buffett isn’t exactly known as a club-carousing party animal. But he was one of the first to arrive at the reopening of Jay-Z’s 40/40 in the Flatiron District Wednesday night. Flanked by two female co-workers, Buffett was overheard telling fellow guests that his blue tie was a gift from Jay, who had been wearing it at the time but took it off and handed it over after the mogul complimented him on it a few years ago. Buffett joked, “I hope he doesn’t want it back.” Buffett invited Jay to his annual Berkshire Hathaway shareholders’ shindig, but admitted, “It’s not quite as good of a party as this.” The Oracle of Omaha stunned onlookers when he posed for photos handing his wallet to fellow guests, with one witness telling us, “Despite his wealth, his wallet wasn’t that fat.” Other guests included Yankee CC Sabathia, who had just come from a Knick game and told us he’s been spending the off-season “watching basketball.” Sabathia joined Knicks Mike Bibby and Tyson Chandler and Detroit Lion Ndamukong Suh, among others, in the VIP room. Samuel L. Jackson made a late appearance at 1 a.m. And while there was no sign of new mom Beyoncé, other guests included Ashanti, Fabolous, Questlove, Swizz Beatz and Russell Simmons. Giants players, including Victor Cruz and Osi Umenyiora, had been expected, but were told by the team to stay in and focus on Sunday’s NFC Championship game in San Francisco.