As with Lisabet, I had a hard time with this topic. Go figure. I've written characters who were obsessed with spanking, rope bondage, rubber, punishment enemas, etc. but that's them, not me. None of those are go-to scenarios.
I guess my deep, dark secret is that the topic I return to is connection. Gay, straight, ménage, whatever, what turns me on like nothing else is that moment of understanding between characters that seems boundless and complete. Bared souls mean so much more than flesh. It's as naked and vulnerable as a person can get.
You can sit next to a stranger on a train and pour out the truth on them like you'd never dare share with someone you knew because of the illusion of safety. (You'd do this for family problems, but if you started talking sex, they'd probably call the police.) No matter what judgment that person forms of you, it's not as if you have to face him/her again. The stranger has no emotional investment in anyone you talk about, so they can be completely impartial. And the best part is that when you reach your stop, you can waltz away unburdened.
It's a weird situation when strangers are safer emotional witnesses than lovers, but complete honesty with someone you know is risky as hell. What if they are so disgusted that they walk out of your life? Or worse, stick around and make your life miserable? That fear keeps us silent. In a perfect world, the person you love has your back. They want you to be happy. They want to be allowed inside your heart. Many people needlessly fear an honest sexual conversation with their lover. That makes me so sad. I'd love to dare everyone to make a sexual confession to their lover, but I know that isn't practical. Sometimes, the fear of rejection is spot on. That makes me even sadder.
In my stories, sexual honesty always turns out well. That's my obsession. Maybe it's not kinky, but in real life, opening up like that is the most dangerous and edgy thing anyone can do.