When a man meets a woman wearing a low-cut dress or blouse, is it rude to momentarily glance down (not stare) at her cleavage?
It isn't rude to her. That is exactly why she wore it - to get attention. Now, there may have been one or two people in particular whose attention she was trying to get, and as such, she may be uncomfortable with you taking a look. But tough toenails for her. She doesn't get to pick and choose if she goes out in public like that.
It may be rude to your wife, depending on how obvious you are about it.
Most men find this a natural, unavoidable impulse.
True. This is the way our biology is wired.
Dear Abby gets gender partisan:
It may be a "natural, unavoidable impulse," but gentlemen have learned to control their impulses.
And ladies know exactly how they are dressing.
I'm surprised you haven't heard the phrase, "My eyes are up here."
I would suggest completely ignoring any woman who behaves this way. She is an attention whore, and wants attention so that she can then insult or hurt others. Ignoring women like this drives them even crazier than they already are, but you should do it for your own protection.
What other possible reason, other than to draw attention to her breasts, would a woman display her cleavage to strangers in public? Women, if you're going to dress this way, the appropriate response when you notice a man noticing that you've dressed this way is to smile.
I had a girlfriend who was sporting DDs (beautiful... just glorious marvels of nature), and she wasn't overweight in the slightest... she had the perfect body as far as I was concerned, but like most very attractive women, she didn't see herself that way. She was a teacher, teaching middle schoolers at first. She dressed very conservatively, and yet heard from some of the girls that they thought she was purposely showing off. Nothing could have been further from the truth. That is not what is going on this letter to Dear Abby. Anyway, my girlfriend asked me about calling up boys to the front of the room to do work on the board, and it there was a problem with that. I told her at that age, boys are "at full attention" quite often, even if there is no present visual stimulation. But with her there, it must have been going on constantly. She took my advice... best not to have the students get out of their seats.