Are fantasies always your own, or do you develop them when other people tell you theirs?
I seem to develop them from others. You know, start thinking about it, turning it into a scene, a story, something juicier. Put in a couple of nameless, faceless people and the fantasy heats up. My girl is almost always kind of naive and shocked by things, so this kind of steams it up a bit too.
But no matter how much I borrow someone else's fantasy, I do come back to mine, just for me.