I have seen it before actually. These days, if a woman caught me staring at her chest, chances are I was staring for a good reason which is usually some low cut top. Women know what they're doing but the key thing is not to be embarrassed because you were staring. Own it, smile, and move on if she gets offended. Remember, women like that only get offended when a guy she isn't attracted to is staring at her. But as soon as some guy like Brad Pitt stares at them with mouth open and drool visible, she'll gladly take her top off.