> You don't know that.
No we don't. But we do know the other people in the office made jokes about the manager telling the author to cover up. I think they might have shared a "Don't feel bad, she told me to cover up too" story if they had been told that.
> In general if dress codes are sexist, they're sexist against men.
Most offices I have worked at do not require men to wear suits and ties. Also, if you wanted to wear a skirt management wouldn't be able to get upset at you unless your contract specifically said you would follow the company dress code without a lawsuit. Also, I've seen men wear kilts to an office before, and that's also a protected class.
I don't know what you are talking about here.