When not fulfilling his vice presidential duties or making another gaffe into a microphone somewhere, Joe Biden likes to, er, skinny dip. In a new book, “The First Family Detail,” which spills the secrets Secret Service agents learn about the people they protect, Ronald Kessler writes, “Agents say that, whether at the vice president’s residence or at his home in Delaware, Biden has a habit of swimming in his pool nude. Female Secret Service agents find that offensive.” Biden might be a tough assignment, but he’s not as bad as Hillary Clinton, who is regarded by Secret Service agents as the worst person to protect. More…