Yeah, the being careful what you say about people in your own life is very important.

Even a stranger on the street is fair game. One of my favorite games back when I was dating a guy who got off on the fact that I like girls, too, was to sit on a bench in the mall and whisper in his ear all the naughty things I'd like to do to random pretty girls that walked by. The idea of me kissing an actual friend of ours, however, was too much for him.

Using fantasy to spice up relationship = good.
Same fantasy carried far enough to destroy relationship = bad.