Short Answer: Never. Is he stupid? Did his mother drop him on his head?
Question: What can be done about naked pictures posted without permission on a social networking site? A few years ago a computer was stolen which contained naked pictures of someone I know. Now that person has taken photos from that computer and posted them on Instagram. We know who has done it, name and place where this person lives.
Answer: This is a big no-no for anyone to post. The Internet is such a huge unwieldy monster that posting naked photos without someone's permission can result in a very large damage award and probably criminal charges. You need an attorney to send a letter to the person with the photographs and you need to do it quickly.