At the moment, men are marrying later than women, and chasing overseas brides. Brides sometimes come from Vietnam, where the girls outnumber boys and the culture is somewhat similar; also men occasionally marry African women, as China is now doing more business there; though there's a hell of a lot of racism in China towards anyone with darker skin than average. Also, men are expected to buy a house and car before marriage, which isn't great for men from poorer families (the boys parents usually foot the bill, as few men in their 20s can buy a house). Actually, the costs of male children is starting to reduce the prejudice a bit.
It will raise the crime rate, and cause social disorder (young unmarried men are the kind of people who throw molotov cocktails at authorities - and no authority wants that). China knows this, and has softened the one-child policy a lot. Women used to be forced to abort subsequent pregnancies; now they are more likely to face a fine. Also, prostitution is widespread.