Man, nsfw it. I was on the train and when I saw this I had to start furiously masturbating. Everyone else gave me strange looks and were saying things like “what the fuck” and “call the police”. I dropped my phone and everyone around me saw this image. Now there is a whole train of men masturbating together at this one image. This is all your fault, you could have prevented this if you had just tagged this post NSFW
I think it has a lot to do with what the sender wants to get in exchange. Men often want that primal, purely sexual "Look at my naked body," and assume that must be what women want too, to just see naked sexy bits.