I guess it depends what fetish, as I have many!
My personal favourite fetish/perversion (delete as appropriate!) is enforced male chastity and orgasm denial, which includes the wearing of a chastity device such as the CB-6000.
I had been into Female Domination and male submission since my teenage years, through flirting at school during which the girl would be dominant and I submissive. This was my first fetish discovery, which would follow on to others.
Many years later, I read about enforced male chastity and orgasm denial, and I also learnt of the existence of the CB-XXXX range of affordable and user-friendly male chastity devices. I was turned on masochisticly by the thought of orgasm denial enforced by the wearing of a chastity device!