I wouldn't tell a family member that BDSM interests me. They think RENT is too scary at the theater...
I don't think God has a sense of humor about the darker side of my fantasies, and sometimes I wonder if I'll have to pay very dearly in the afterlife.
But I'm a talky bastard, and I would no doubt talk in a hushed tone on a bus if I happened to be sitting next to someone who had similar interests.