Subtle sexism is so precarious because it is thought-provoking — for the targets. Management and psychology researchers Dr. Eden King and Dr. Kristen Jones have found that implicit biases can actually be more harmful than outright discrimination for several reasons, including: the higher frequency with which they occur, the lack of clear legal recourse, and the amount of time women spend analyzing these perceived slights.

A former Congressional staffer writes about sexism in the Athena Talks blog on Medium. 

This quote has interesting parallels to racism.

To be clear, this concern over sexism in the workplace was not part of my experience.