Ethics on Applying Makeup at the Office Restroom?

I wouldn't worry about what anybody else says to you in this regard. Wearing make-up and putting it on in the privacy of a business washroom is your business and its personal. Having to share this kind of space is just how it is when many people work in the same office or building. You aren't bothering anyone else and it is not an offensive act, so don't let the other women get to you. There are lots of reasons why people complain about such trivial things, but they just might stop if they could walk in your shoes for a few days.