In the Horny Worlds, everyone is horny and sexually open, but not in a free-use society. Natural and real-life laws and taboos are still in place but they are often bended and/or broken in secret for the pleasure of whatever naughty act the deviant in question wants. Incest is common but not spoken about, married men and women often cheat and swing on each other, and "rape" is not really rape. This is just the general setting though, the way people act in the world depends on what world they live in.

(Adders, feel free to make fanfictions using this idea)