While plenty of people came out to see actress/designer Olsen, it was Mizrahi and Givhan who stole the show, squabbling in a good-natured way about everything from too-skinny models to platform heels.
On the great weight debate, the always hilarious Mizrahi explained that designers use super thin models, "Because it works!"
"Fashion advertising is hurtful," he said, "but somewhere it works, which is a sad statement... Ok, somebody sing something!"
After the crowd erupted in laughter, he tried to explain it some further, saying, "It's like making this amazing soufflé and then are you going to serve it on Earthenware or on a gorgeous platter?"
While Rivhan tried to defend normal-sized women everywhere, exclaiming, "I am not Earthenware!"
Olsen, for her part, talked about the stigma of being a celebrity designer, but claimed that she and her sister are a unique case.
"I think some celebrities think of a fashion line as just adding to their brand. But we grew up in the entertainment industry and being an actor was not what I dreamed of being when I grew up," she said. "When I turned 18, I stopped and thought about what I really wanted to do."
And, as we know, what she wanted to do was fashion. She's now running two successful companies that are up a combined 30% this year: high-end line, The Row, and the more accessible Elizabeth & James label.
Overall, she says, The Row has nine employees, while Elizabeth & James has thirty, although the Olsens don't oversee the latter, since it's a licensed brand that they mostly do consulting on.
We also found out that Olsen doesn't plan on returning to acting anytime soon, and, much to the chagrin of Leive, says she doesn't pay much attention to the media.
"I don't go on the internet or read magazines," said Olsen. "I block it completely."
As the evening went on, the panel was asked about their current favorite trends, which all, oddly enough, revolved around footwear.
"I love low heel shoes!" declared Mizrahi, while Olsen said she was digging comfy Toms footwear and Givhan revealed she was still loving platform pumps, which Mizrahi deemed "boring."
To wrap up the discussion on everything from the "Michelle Obama Effect" to how they picked out their own outfits for the evening, Leive asked the group to leave by answering one big open ended question, "In the future, fashion will be more...."
"Democratic," said Givhan.
"Exciting," said Olsen.
"Less obvious, less visual, more about fetishes" said Mizrahi, cryptically. "It'll be more like tiny crazy trends that no one perceives or understands."
Do you agree with any of them? Tell us how you see the future of fashion in a comment below.
And to see what happened backstage at the event, including Olsen fessing up to her stage fright, head over to Glamour.com.