EDIT:
I did not mean to say that being passionate is bad. I meant to say that in most social situations, appearing overly passionate is often bad. Right now, I am struggling to maintain passion for the project I'm working on and I know that I will fail as soon as I stop being passionate about it -- so I know there are hard times when passion is necessary. However I think that my point about appearing "cool" holds -- more people get excited about my projects when I put up an impression of total control and slight lack of passion rather than the other way around.
One has to know how to program both oneself and others.