Obama's reason to stop smoking: His daughters

She said that when the topic turns to smoking, "we're very clear. It's not good for you. It's addictive," and that the president used himself as an example.

"But I think he didn't want to look his girls in the eye and tell them that they shouldn't do something that he was still doing," she said. "So they played an important role in him finally saying, 'I've gotta get this done' ... he credits them with that."

The first lady said that it's important for her and the president to be "honest and open" about their imperfections with their daughters, to show "we're not perfect adults."

The sit-down with the Internet site comes on the heels of other lighthearted interviews with the Obamas — including with People magazine and on "Entertainment Tonight" — aimed at highlighting their relatability. A new NBC-Wall Street Journal poll shows that Obama leads Romney by 35 points — 58-23 — on the question of who's more likable.