You've been programmed to think this is bad, unhealthy or unnatural by people with an agenda. There's another school of thought that says it's ok, normal, natural, and healthy. Humans are hard-wired for sex and we've been having sex like rabbits for millions of years otherwise we wouldn't be here. There are many situations and places and modes where we pretend it doesn't exist, but it's a lie, at best a convenient intellectual abstraction in order to focus on productive matters. But it's always there, lurking. Again, for most healthy people it is anyway.
Now, if anything, I over-correct when I'm talking to someone who I find attractive and is wearing a very low cut shirt. Eyes. glued. to. eyes.
No I haven't. I don't think it's the least bit bad or unhealthy. I simply want to engage my friend as a friend, not glance at her tits every ten seconds. Performing physical actions that imply attraction would introduce a power balance that I don't want in a friendship.
I have been in that situation years ago, and I remember it to this day. It didn't help that I was much younger then.
Anyway, I found it incredibly hard to concentrate on what she was saying, because I was concentrating on keeping my eyes away. It didn't help that she was absolutely gorgeous, well-endowed and was wearing a dress with a cleavage probably modeled after the Grand Canyon. Thankfully, she was not a coworker. But even worse, she was a potential client.
I don't want to be too quick to blame it on instinct, but it is there. I wonder if I were (proportionally) as well-endowed as she was, and wore tight shorts. Some female friends told me that they do look - but women seem to be more discreet, on average.
Is this sexism? Or just normal human behavior?
Sexism would be if your attraction influenced your professional behavior towards your prospective client in any way, negatively or positively.
As you hinted, being able to be less distracted by an attractive figure is a matter of self-mastery, which often comes more easily with maturity, and to some degree familiarity. But a modern gentleman knows to treat others as persons first, not as sexual beings, especially in a professional context.
So, I'm not going to agree or disagree with you, since I don't really know exactly what you're saying.
I will say this, though: there is professional attire for women. Generally speaking, this doesn't involve form-hugging clothing. A fitted women's dress shirt is not form-hugging, by the way.
Personally, I recognize that I have an unfortunate automatic physiological response to breasts. I've discussed this with female friends whom I've respected and liked strictly as friends. If exposed to low-cut tops, I find my eyes darting to them, particularly when I'm distracted or concentrating on some thought. If I were in a position where a well-endowed female coworker were wearing very snug or revealing clothing, I'm honestly not sure how I would handle the situation.