Scientists have observed that it is usually a woman who gives the man subtle body language queues that it's okay to approach and talk to her. In my experience, the quickest way to make a woman livid is to be given the nod or the smile indicating that you are now "allowed" to talk to them and then ignoring them. Their body language goes totally cold and they sometimes will even make a rude comment. I call this the "pretty privilege." Pretty girls expect or assume to have a certain power over all men that they are interested in.*

Just another example of how confusing our culture is right now. The rules might have changed but the biology stays the same.

*caveat that not all women are like this or are even aware that they do this.