Attention is a double-edged sword.
If a woman says, "I am going to put on my sexy little number and show some cleavage", what she is really saying is..."I am going to put on my sexy little number and show some cleavage."
She might wear it for the sole purpose of turning male heads, or she might be wearing it because she likes it, because that's the kind of style that looks good on her, because she is comfortable in her skin and/or proud of her body, because she spent the week hanging out in cargo pants and hiking boots and wants to feel sensual and womanly, because she is going out with fashionista girlfriends and wants to fit in, because she's going to a hot nightclub that only lets in the sexy people, because her style icons are Brigitte Bardot and Sophia Loren or the pop star or some other It girl of the moment.
She might wear it because she grew up in a culture that worships supermodels, because short skirts are in fashion that season, because she just bought the dress for fifty percent off and wants to wear something new, because she spent the past five months in the gym and is proud of what she's achieved, because she "got her body back" after having a baby (or babies) and wants to celebrate getting out of the house.
She might wear it because she's defiant and rebellious enough to want to flaunt her female form instead of feeling inferior just for having one in the first place, because clothes are fun, because she's experimenting with her identity, because her more demure going-out outfit is at the drycleaner's, because women get judged and criticized no matter how they look and what they do and what they wear so she just decided Fuck it, because she's in an environment where she feels safe enough or confident enough to be "provocative" (i.e.: she has faith that men are not animals and won't harass or assault her).
A lot of women spend most of their lives tamping *down* their natural sensuality (how they like to dress, or move, or dance, or talk and laugh with strangers) because they know they'll be slut-shamed or even physically at risk if they don't. In other words, that sensuality still exists even when there's no man around to respond to it. A lot of men (and a lot of women also) think that it's okay to disrespect a woman -- treat her like less than a human being -- just because she's any degree of sexual. Sometimes she doesn't even mean or want to seem "sexual", but like Jessica Rabbit once said, "I'm just drawn that way."
It's probably not the fact that you're looking at her, but *how* you're looking at her, that offends. Maybe your body language conveys something that you don't consciously intend.
The difference between desire and objectification: whether you respect the fact that the person you look at can look back.