Admiring a Woman

If a woman has a low-cut top or very short skirt on and is showing some of her body, is it rude to look? I don't really think so. It is different than a situation I was in a few days ago; I was walking the dog and a woman was collecting her mail wearing only her nightie, which was low cut with big arm holes and she was showing plenty of breast. I looked, she saw me looking and covered up. I was embarrassed and looked away. What else could I do?

— Tom, 70