It is never appropriate to comment on a woman's breasts. I would never do it on the street or at a supermarket, but when I'm sitting a table signing books, sometimes I notice that a woman will have remarkable breasts. And I will maybe quietly say something about it. It's not in a sexual way, because I'm a gay man - I would never say to a man "great ass" because that would be sort of creepy.. I hope it's not creepy to quietly tell a woman she has nice breasts.