This is an idea I've been itching to write. How it plays out, and the characters/genre involved, can be very flexible. I want the pairing M/M, though I'm female myself and I don't care if the other writer is themselves male or female. I write with characters, I'm not worried about the bitss on the other end of the connection. But here's the basic idea (I play the prostitute).
A male(not necessarily human) is working in a high-end brothel. It's a secret life he is hiding from others who know him, he is only there a few days a week. He's pansexual, very adventurous. One day someone he knows (either a close friend or a fierce enemy) comes into the brothel as a client. This person is shocked to see this person he knows working in such a place, but decides (for whatever reason) to hire the man and have his wicked way with him.
How it plays out obviously depends a lot on the people involved, their relationship, and the reason for one hiring the other. The characters involved can be human or not, the setting anything from fantasy to historical to futuristic. (Though I have to say I prefer dealimng in a setting where we don't have to worry about safe sex, so some sort of non-strictly-reality based setting is preferred.)