I can't quite put my finger on a consistent theme in female millennial clothing (except that they don't dress like me.) But I can tell you that they must not invest heavily in hairbrushes because their hairstyles look like they used their fingers as combs and brushes.
I see young women on the train everyday and at work who just have messy hair. Not intentionally messy hair. Just messy hair. Like they didn't comb it, didn't blow dry it, but instead just pulled it back in a messy ponytail with bits and bobs sticking out. Forget a sleek chignon. They have lumps and bumps all over what should be smooth pulled-back hair.
It drives me crazy at work to see hair like that. You're in an office, not the gym, for crying out loud.
So invest in a cheap brush and use it. And while you're at it, buy a bear of tights and use them when it's 30 degrees outside. We all realize your spray-tanned legs are gorgeous in those 4" heels, but you're going to catch pneumonia walking in the polar vortex with all that skin exposed.