According to Americablog, those men were actually members of a coalition formed by the French Catholic Church and a right wing political party called UMP. They're fighting gay marriage, but they're pretty late to the party, since gay marriage was legalized in France a month and a half ago. Apparently, that's not stopping them. The French who oppose gay marriage have different ways of showing their disapproval, but the Catholic Church/UMP coalition's preferred way is to send men in various states of undress out into the street to publicly protest, because that doesn't seem counterproductive at all.
Here's the replay from a couple different angles: