The degree to which a perceived authority, i.e. mpaa, pope, and usda, believe a thing should be accessible to children.
According to a great many early christians and judaists, and many modern muslims, non-consensual sex with a pre-pubescent girl was of a high degree of family-friendliness, as long as her owner was the partner and all viewers and participants were members of the household.
United States culture generally says that vegetables have a low degree of family-friendliness, compared to high sugar or sugar-substitute foods.
As long as euphemisms and discrete phallic pictures are all that the movie references to sex, the mpaa will consider giving the movie a g rating for family-friendliness.