The 30-year-old revealed how the gown she wore to sister Kate Middleton's marriage to Prince William in 2011 transformed her life during her first public speech.
"As I have found out, recognition has its upside, its downside and — you may say — its backside," Pippa joked at a dinner held by Women in Advertising and Communications London group.
Revealing that she was so nervous before her sister's wedding that she didn't sleep for two days, she said of her bridesmaid dress that she was just "glad it fitted" at the time, but added, "In retrospect, it fitted a little too well!"
Around 400 people attended the dinner, which was held at London's Savoy Hotel.
Many were surprised by Pippa's candor, as she admitted that accusations she was cashing in on her royal connections by writing a book and magazine columns had hurt her.
Pippa said she received a negative response to her book Celebrate
She also said that the negative response to her party planning book Celebrate — which only sold 18,000 copies — had been "difficult".
"It was the first time she's made a speech of this kind, but you wouldn't have known it, she was so relaxed," one guest told the Mirror. "It was unbelievable how open she was — I don't think anyone was expecting that.
"She talked about the royal wedding and her career since. She came across as really grateful for the opportunities but also talked about the pitfalls of her position."