Much has been made of the fact that this is the first Olympics in which every country sends both male and female competitors. And with the introduction of women's boxing, it is also the first Olympics in which there are no men-only events.
Synchronised swimming remains exclusively female, however, and within sports, there are many disciplines which are only open to one gender or the other. But as this video, via Reddit, shows, there may be a reason why men rarely do the uneven bars. It involves an awful lot of hits to the crotch (I presume the "hilarious" drag is not actually required):