A bit lighthearted as it doesn't really bother me just makes me a bit 
My DS is 2 and has longer hair, (think suite life of Zack and Cody) it stops just as his tshirt collars start at the back.
Sometimes it's down and sometimes we put it up I suppose in a bit of a 'man bun' style. (Especially when he's running around to keep it out of his eyes)
These past few weeks I've noticed when we are out in public people refer to him as a boy if he has his hair down and as a girl if it's up. It happened about 3 times yesterday.
I don't really correct them as it's usually in passing e.g. Mum saying to her DS "watch out for that little girl" or yesterday he was playing football with a few older boys and some his age in the playground and chased on of the boys his age and the dad went "look at that little girl chasing after Jack".
I know it doesn't really matter that much but he was wearing jeans, trainers and a blue top with a dinosaur on it.
Yet people ONLY ever do it if his hair is up. When it's down he's always referred to as a boy.
AIBU to think that this is a little bit weird of an assumption to make based on a hair style?