Take pictures of women at work with their hair down. Discreetly. With their permission if possible.

File a formal grievance form, and keep a copy.

Then let the matter drop for the reasons you listed earlier. Now there is documentation to back you up if something happens down the road. People can "forget" conversations. It is absolutely illegal for them to do anything to you in retaliation for filing a grievance. The more incidents you document, the easier it will be to demonstrate to HR (or a lawyer, though it probably does not need to go that far) that A) you were mistreated, and B) you were mistreated in reaction to your complaints about mistreatment.