velour, great post, exactly something I have been trying to express (to myself mainly).
Hair length: Long hair can be very 'masculine'. Many men wear long hair and it doesn't make them the teeniest little bit feminine. They are not expressing their 'feminine side'. There is nothing about long hair that is intrinsically related to 'female'. As soon as men choose to wear long hair, long hair becomes one way of being male. Just like short hair is one way of being female.
Same with colours. Pink is for girls blabla, no, a man wearing a pink shirt is not 'feminine'. Wearing pink is one way of being a man. Just like wearing work trousers is one way of being a woman.
I have a feeling though that in the last 10 - 20 years or so, things have become more, rather than less, attached to sex. Especially for children, in that toys and clothes and even books have become very distinctly coded for either girls or boys, making us and our children believe that when a boy plays with a pink pony, he is playing with a girl's toy, not just a toy. My children, if they wear trousers to school, they wear boy's uniform, not just uniform (my daughter would be breaking the uniform policy; all primary schools here restrict girls to skirts/dresses and boys to trousers). If I get a book about strong women, it may actually say in the title that it is 'for girls'.
I then find it not very surprising that teenagers who are working out who they are and have learned throughout their short lives that certain things - lots of things actually - are 'for girls' or 'for boys' (e.g. due to school uniform policy of 'boys must wear their hair short' they will rarely, if ever, have soon a boy with long hair) get confused. If pink is for girls, and I love pink, if I am a boy it is easy to be confused and perhaps conclude that I am not a boy after all.
It is a bit late then to start explaining that pink is for everyone, and it is perfectly fine to be a boy and like pink, and that wearing pink doesn't make you feminine, because there is nothing intrinsically feminine about pink. This has to start way earlier, with toys, the clothes we put on our children, the school uniforms, the activities we encourage our children to do. The things we praise them for.
But I worry that individually doing this right is not enough - our children learn from their peer environment, and for us at least this is incredibly strongly gendered (as in, all manner of things are associated with a sex - e.g. pink is a gendered colour because it is associated with the female sex, it is this association with sex that constitutes 'gendering' IMO), so no matter how many times I say to DS that colours are for everyone, he can't fail to notice that no boys wear pink clothes and no boys play with pink toys (they - and he - used to, up to about age 5 or so, but no longer, except perhaps in private/secret).
So it requires a wider movement, IMO. If 'things' (clothes/colours/personality attributes/interests/...) lost their association with a sex, then men wearing dresses and boys liking dance and girls doing engineering and women dressing in pragmatic workers clothes would be just that, and have nothing to do with gender-nonconforming nor with trans-gender.
Far from 'gender does not exist', I think that, sadly, in our society gender is stronger than ever, with more and more 'things' becoming gendered, not less.