It's pretty simple, but very disturbing, why so many people think it's ok for a girl to like 'boy' things but not for a boy to like 'girl' things. And that's because on a subconscious level we think the girl is 'aiming up' by wanting to be like boys while the 'girly' boy is aiming down. I used to fall into that trap myself when I was younger. I was a tomboy and I thought that made me better than other girls who liked 'stupid girly' things. I didn't realise what a disservice I was doing my own gender. It's like the opening lyrics to the Madonna song, What it Feel Like for a Girl.
Girls can wear jeans
And cut their hair short
Wear shirts and boots
'Cause it's OK to be a boy
But for a boy to look like a girl is degrading
'Cause you think that being a girl is degrading
Girls can wear jeans
And cut their hair short
Wear shirts and boots
'Cause it's OK to be a boy
But for a boy to look like a girl is degrading
'Cause you think that being a girl is degrading