I was going to mention Wraeththu, but then I reread your entry. Although they are hermaphoditic, most of the Wraeththu start out as human males, so I don't think it quite fits.
There's also the real-life story that Monster (2003) was based on (also see the title of the movie).
This story is also not quite what you're looking for, but I think I'll relate it anyway. In the movie/play "Suddenly, Last Summer", the main character is being institutionalized for witnessing something her aunt wants to kept secret. It is revealed at the climax that while on vacation, her cousin was murdered and eaten by some young men that he had paid for sexual favors. You know from the beginning that the cousin is dead, so I kept wondering what horrible thing he had done that his mother was trying to hide. I thought he was a serial killer or a monster or something horrible. I was confused and let down when the big secret turned out to be that he was homosexual. Frankly, I think she would have been less ashamed and horrified if he had been a murderer.
Spoilers for Suddenly, Last Summer
There's also the real-life story that Monster (2003) was based on (also see the title of the movie).
This story is also not quite what you're looking for, but I think I'll relate it anyway. In the movie/play "Suddenly, Last Summer", the main character is being institutionalized for witnessing something her aunt wants to kept secret. It is revealed at the climax that while on vacation, her cousin was murdered and eaten by some young men that he had paid for sexual favors. You know from the beginning that the cousin is dead, so I kept wondering what horrible thing he had done that his mother was trying to hide. I thought he was a serial killer or a monster or something horrible. I was confused and let down when the big secret turned out to be that he was homosexual. Frankly, I think she would have been less ashamed and horrified if he had been a murderer.