President Obama on Monday indicated he rather likes Supreme Court Justice Ruth Bader Ginsburg's nickname, and called her one of the tougher justices on the Court.

He noted that in the crowd of about 175 was "arguably the toughest justice of the Supreme Court [who] is [also] the oldest ... Ruth Bader Ginsburg ... also known as the 'Notorious RBG,'" he joked, riffing on rapper The Notorious B.I.G.'s nickname.

Bader Ginsburg has enjoyed the nickname for the last several months, and a website has even been created celebrating the name.

"She's tough," he said. The Notorious B.I.G., whose real name was Christopher Wallace, was killed in a drive-by shooting in 1997.

Obama spoke at a conference on aging at the White House, where he also said no one should challenge senior swimmer Diana Nyad to a race. "You do not want to race her in anything," he jested.

The 65-year-old Nyad, who in 2013 became the first person to free-swim from Havana, Cuba, to Key West, Fla., was also on hand for the conference.

He also joked that he hopes to be part of the trend of older Americans contributing to society well past retirement age.

"Since I'm living out dog years here in the presidency, it's ... this is something I'm paying a lot of attention to," he laughed. "Look at this hair," he said, pointing to his graying coif, "although I do have hair. Crowley was laughing a little bit too much there," he said, referring to balding Rep. Joe Crowley, D-N.Y., a top lieutenant to House Minority Leader Nancy Pelosi, D-Calif.