Is there really exist a line between masculinity and femininity?

These days, we often concentrate on the topic of the hegemonic masculinity and the subordination of femininity. I feel like maybe the difference between male and female, regardless of the biological structure, is not that vital. The blur of sex is especially obvious in fashion industry. I recently notice a male  model whose name is Andrej Pejic. If I was not told the model is a male, then I certainly will regard him as a girl. Andrej even becomes the spokesman of female underwear! This is what I have never heard before. But if women can dress themselves as men, asking for equal rights, why men can never wear a bra? Isn't it an unequal treatment? Now,  as we can see, some male models follow Andrej, also acting in a feminine way but keep their masculinity at the same time. Therefore, we may expect the equality arises from fashion industry and gradually influences other places.