Believe it or not, thanks to a law passed in 1799, women are forbidden to wear pants in Paris. The law was amended in 1892, allowing women to wear pants if they were holding the reins of a horse, and again in 1909, if they were riding a bicycle.
Interestingly, female policemen (gendarmes, if my French is correct) wear pants in Paris, so technically, they are all breaking the law.
Over the decades, attempts to take the un-enforced law off the books have failed, even as late as 2003. But it looks like it might be repealed.