SWEET AND SOUR
A person perceived as female must rely on their appearance, as it has dramatic control over their life. Beauty and charm are considered to be the weapons (or lack thereof) available to a woman; women being vain is a tool of protection and self-preservation. It is even considered unnatural when a perceived woman seemingly does not care about their appearance. And, should they begin to fall subject to traditional femininity such as indulging in makeup and feminine clothing, they are deemed as ‘growing up’ or somehow becoming more attractive.
This subjection to praise for appearing traditionally feminine, provided by both women who value tradition and the male gender, fuels this female vanity. Because of this truth, it is impossible for vanity to ever be unrelated to femininity, and for femininity to be unrelated to vanity. They must coincide.
It is also important to note that men who are perceived as vain are usually also considered to be less masculine, hence further solidifying that vanity is feminine.