In the late 1770's, an insignificant event took place that was completely blown out of proportion, causing another chink in the Queen's reputation. Marie Antoinette loved the theatre. She loved the music, the entertainment, and that she could, for a few moments, behind the mask that was the fashion, act as if she were a normal person leading a normal life.
So, one evening...
Marie Antoinette and the Duchesse de Luynes, set off for the theatre. Traveling light - probably with a pared down number of servants accompanying them. Entering Paris, her carriage broke down and she and the Duchesse had to take refuge in a shop until a fiacre (named as such after the Hotel de St. Fiacre from which trotted the first of the horse-drawn taxis), ordered by a footman, arrived to transport them the remainder of the way. No material for scandal there. She could've gotten away without everyone in town knowing about it, but for her telling the story to her friends. One can just picture her bursting into the theatre in giggles, excited to have had a break in her over-scheduled, over-supervised life. In her memoirs, Madame Campan quotes Marie Antoinette as laughing about it, saying "That I should be in a fiacre! Is it not droll?"
The story was mildly amusing, but so much improved by the re-telling. Madame Campan wrote, "From that moment, all Paris was informed of the adventure of the fiacre. It was said that everything connected with it was mysterious; that the Queen had kept an assignation in a private house with the Duc de Coigny...." Those French were like a bunch of bitchy high schoolers.
The masked ball scene from the Marie Antoinette movie starring Kirsten Dunst. Pretty movie, but don't rely upon it for facts.