New York Mayor Michael Bloomberg shocked onlookers when he openly admired a woman's derriere, saying "Look at the a** on her", a media report said on Tuesday.
An author who was introducing himself to the politician said Mr Bloomberg ignored them while looking at the woman, the Daily Mail reported.
Writer Jonathan van Meter related the anecdote in the New York Magazine.
"My friend thanked him for his position on gun control," wrote Mr van Meter.
"Without even acknowledging the comment, Bloomberg gestured toward a woman in a very tight floor-length gown standing nearby and said, 'Look at the a** on her'," he said.
The article did not name the woman.
Mr Bloomberg, 69, is known for his outspoken comments.
In 1996, three years after divorcing his Yorkshire-born wife Susan Brown, he told The Guardian: "I am a single, straight billionaire in Manhattan. It's like a wet dream."