Contemplating the outcome of 60M+ single men (discounting homosexuals which estimates put at around 5-20% of the population) unable to find a woman simply because of the numbers game seems coupled with the "Little Emperor" phenomenon that was discussed here on HN recently is pretty concerning.
In countries with high rates of sex-selective abortions, I fear violent crime rates, particularly sex crime, will skyrocket.
Surprisingly enough, China still has a huge number of (as they put it) "left-over" women. This is likely because the population of there is well aware of the 60M+ fact going in their favor and, in truly amazing display of classical economics, heightened the standards and criterion the average girl uses to look for a man. The result (aside from the large majority who are one-to-one dating/engaged/married like it's always been) is that there are a ton of frustrated young men who (unless a miracle occurs) will remaining single until he dies, a small population of ultra-successful men who concurrently juggle multiple girlfriends (and possibly wives), and a large group girls who are annoyed that all the "good" men are taken.
Unfortunately, sex crimes have been on the rise in China.
With birth control and condoms, there are only cultural barriers to new social norms regarding females with multiple partners. Such behavior is certainly within the range of commonly observed human sexual behavior. Legalized and effectively regulated prostitution would be one way of addressing such a demographic issue while avoiding crime and human trafficking. Legalization would probably be one of the easiest changes to implement. (Given the vehement opposition to such an idea in the US, that's saying something.)
Female infanticide rates (which account for the population imbalance) are correlated with security in terms of warfare and standard of living. Fix those, and the populations will move closer to parity. It's been that way for as long as humans have.
Homosexual population is more like 1-5%. Distinct category from "anyone who has had a homosexual experience or thought" where the larger numbers usually come from. Latter would not be useful here.
In countries with high rates of sex-selective abortions, I fear violent crime rates, particularly sex crime, will skyrocket.