Michelle Obama broke off in mid-flow during a speech to march up to a gay rights protester who was heckling her.
The US first lady told Ellen Sturtz: ‘Listen to me or you can take the mic, but I’m leaving.’
She was greeted with cheers after putting the 56-year-old in her place for interrupting her talk about giving children a brighter future.
But lesbian Ms Sturtz – who shouted that laws should be passed to protect gay people from discrimination – said she had been ‘taken aback’ by the confrontation.
‘As the first lady was talking about our children’s future and ensuring that they have everything they need to live happy and productive lives, I simply couldn’t stay silent any longer,’ she said.
‘I’m looking ahead at a generation of young [gay] people who could live full, honest, and open lives with the stroke of the president’s pen.’
Mrs Obama visited the home of a wealthy lesbian couple to speak at a Democratic party fundraiser in Washington which 200 guests paid up to $10,000 (£6,500) to attend.
Ms Sturtz paid $500 for her place as part of a plan by the gay rights group GetEqual to gain access to party bigwigs.
President Barack Obama supports new legislation to prevent employers from rejecting job candidates on the grounds of their sexuality, but it has yet to be passed.
Ms Sturtz said she had been forced to ’live and work in the closet, hiding who I was in order to earn a living’.