How can you say that about Emily? Ali Beardsley makes the GM cuss at least as often. :)
It's not always bad when your GM says "Fuck you." Sometimes we say it because you just skipped to the end of the mystery that was supposed to last a few more sessions, sometimes it's because you use the spells I just gave you to kill my big-bad.
Mostly it's beautiful, because you did something I wasn't expecting and now I get to work around it in real time. It's not truly a collaborative story until you are making my life as the narrator hard, otherwise I'm just telling you a story on rails.