they don't do it because they honestly think we want to see their dicks, they do it to see what we will do when they cross an unspoken and "harmless" but clear boundary. It's a test. If we respond "haha um are you drinking? I think you sent that to the wrong person" then they know they can push our boundaries on other things and get away with it. If we respond "wtf. Do I need to show this to your boss?" then they know we are not the sort whose boundaries they can cross and they will pursue someone else. They are predatory, remember? They are looking for women who don't know how to communicate and enforce boundaries. This happens all the time, this is what #metoo is all about. It's sick. But to fix it, men have to talk to other men. This is a problem of men's behavior, not women's.
Edit: Thanks for the silver. Since this is getting some attention I'll expand. The reason many women don't know how to communicate and enforce boundaries is not some ignorance or negligence on the part of women. It's because our boundaries are always in flux, depending on how safe we feel, and because there are serious consequences to communicating and enforcing our boundaries in the "wrong" ways, ways that do not apply to men, generally speaking.
And, there are infinitely many ways to communicate or enforce a boundary "wrong," depending on the boundary, and depending on the subjective opinion of the man violating the boundary.
And arguably, there is NO surefire way for us to properly communicate or enforce our boundaries, at all. No matter how we turn someone down, some people simply have no interest in accepting a no. You can say no thank you, you can say I don't think we're a good match, you can say I'd rather stay friends, it doesn't matter, there are a whole lot of guys who will become aggressive and violent when rejected, cause and effect.
Do you know why some women laugh at unsolicited dick pics? I don't mean pointing & laughing at the size of your junk or anything, I mean literally typing "haha I don't know about that" in response to your pic? It's an attempt to deescalate the situation, and give you plausible deniability of the digital equivalent of the sex crime of flashing you just committed, to take the hint that we're not interested, and that even if we were, you're being wildly inappropriate. We laugh like that, not because we're amused, but because if we came straight and said "this is the digital equivalent of the sex crime of flashing and you're being wildly inappropriate," things could get very dangerous for us, and we don't want you to become violent. The little "haha" means you are scaring us. It's not lighthearted, at all. We are certainly not aroused. This is why we say that rape is not about sex, but about power. This isn't just about dick pics. This is about you trying to get us to drink another drink, this is about you trying to get us to get in your car when we are walking, this is about the million other things that men pretend are harmless but would be shocked and furious if the situation were reversed for a single day. We have seen what happens when a man gets angry at a woman and it's not pretty. My best friend from college was murdered that way.
So to the men who get mad, because we don't clearly communicate our boundaries and you want us to, or who complain that our boundaries are inconsistent and you want them to be consistent...
We're doing it because we've learned that direct communication with you sometimes gets us killed. Or shunned. Or fired. Or yelled at. Or stalked. Or passed over for a promotion. Or we lost what we were told was a friendship. And yeah, it's not all of you. But it's more than enough. You want us to stop being afraid of you? Stop being scary. Respect our autonomy. Respect our agency. Talk to OTHER MEN about this. They don't do the locker room talk in front of us, we can't fix it. You need to speak up and explain why it's not okay, when it's actually happening. Men won't listen to us, but they'll listen to you.