Well, a bunch of different things would happen, each leading up to progressively more comical outcomes. If a law had indeed been passed mandating that men wore bras, it would instantly trigger many questions of competency on the part of legislators. The foremost questions asked would be: What party backed this proposal? Where did the support come from? How did it garner so much action when there are more pressing concerns such as improving the economy, invading Syria, and reforming Obamacare?
Eventually, an investigation would be instigated by journalists, as the media acts as a particular fourth branch of government checking the other three. It doesn't take more than a few Google searches for them to land on a real rogues gallery of links ranging from fat activism, fetish erotica, an old Seinfeld episode, to deviantART profiles. Eventually, however, the journalists focus their attention to the smoking gun: one Christian Weston Chandler of Ruckersville, VA. A news organization comes across the CWCki, and after running a piece on Chris' highly bizarre nature, concludes that one autistic individual had somehow influenced the entire legal system. Citing the precedence of Terri's Law, in which Florida courts concluded that a law allowing Gov. Jeb Bush to reinsert Terri Schiavo's feeding tube was found unconstitutional, the law is eventually determined as a gross overreach of government passed solely in the benefit of one citizen. A lawyer filing suit against the US Government makes the case that not only is this law a violation of our First Amendment right to freedom of expression, but also that it is a law passed solely with the interest of one in mind and not the interests of all. Without hesitation, the lowest court strikes the law down as unconstitutional. No district attorney decides to contest it, and the matter becomes a relic of a complete legislative fuckup. Estimated time to repeal: roughly 2 to 3 weeks, about the time it takes for a dirty, crapped brief matter to resolve itself the court system given the overhead of paperwork and other clerical duties. With the expediancy of a lawsuit combined with a preliminary injunction halting enforcement of the law, no man would ever end up wearing a bra as the law dictated, before it had been repealed.
But our media wouldn't stop there. How did someone like Chris get to exert so much influence over our legislature? Who is running this whole show anyway? Constant interviews are arranged with the people responsible for this mess. Eventually they are forced to explain their intentions after giving various conflicting answers in the ensuing media hellstorm raining on their office. The most likely explanation would be excessive, child-like pandering to the whims of special needs constituents. This would spark wider questions of "How far is too far?" when it comes to accomidating "special" people like Chris. The self-esteem movement of the 70s and 80s would be castigated as one of our culture's most corrosive endeavors, the legislatiors sponsoring the bill would be forced to resign, anyone who voted for it would be passed over in the next election, and there would be a rather short backlash against people like Chris as Americans don't take too well to things like ceding their own time, energy, and rights to ensure the rights of a minority, especially if it's for something they don't see legitimacy in (for example, gender-neutral bathrooms). Legitimate movements such as transgender rights are set back considerably because people are ever more skeptical to pass laws in benefit of a small minority. In a matter of months, legislation would be passed to ensure something like this never happened again, and after roughly fifty years, it would be found in "Toilet Trivia" books as the 2013 Bra Law.
And of course, in the end, Chris would levy endless accusations that our court system is full of dang, dirty trolls who do nothing more with their time than play America's favourite game: Kick the Autistic.