do women know when their nipples can be seen?

Perhaps they're not ashamed of them.

In the kingdom of the blind, you're the village idiot.

Dropbtrough in the spot and stroke your choke.

Calm down, they're only nipples - every mammal has them.

They do it on purpose to get men's attention. Most swimsuits for women have built-in bras with padding, so if you can see the girl's nips, she's wearing a non-padded swimsuit/suit top on purpose.

Consider this line form the little known film "100 Girls":

Well, take the breast for example. You have the bosom, the areola, the nipple. I mean, those are three concentric circles. In other words, it's a bullseye! It's no wonder the breast is the target for all men.

Agree or disagree: Men spent 100 times more time thinking about women's nipples, then women do.

There may be the rare woman that is clueless about her own body and how her nipples will react when she jumps in the water.... and there may be the rare woman that is clueless about what the swimsuit will look like when it gets wet... but that is insanely rare. Most women know the high beams go on when they get in cold water and most know that thin light materia become translucent when it gets wet... You know most have seen a wet t-shirt contest at a spring break party so it isn't as if they lack simple logic to understand the effects of water on a light weight and light material. They've also noticed that if they are looking at swimsuits in a store that there is a reason they have thicker padding to simulate a bra in them.

Give the above, it can only mean that the women are seeking attention and want to show off their nipples. Which is certainly the reason they post photos of them on facebook where they show. They want to show them off, so be it. The only problem is when they complain that people are staring at them, which really makes you want to say of course they people look you stuck them out on display what the hell did you expect people to do.

Of course they do! One of the lesser-known senses (you've heard of the big five: touch, taste, sight, and there are a couple others, including smell) is the nipples sensitivity to gaze. Men are not quite as aware of this sense as women are, it's probably biological if you had to guess, but sure, it could be nurture as well. The laws sure help with that, that's for sure. Did you know in many areas, a woman can be charged with a crime for showing her nipples whereas a man would not be? That is probably the origin of the expression 'free the nipple'. I'm all for that, actually, although I would also hope that when they free the female nipple, they lock the male one up. For at least 20 years. As a cooling-off period.