Another Question for those who Believe Differently than I Do?

It's almost unavoidable that topics of belief in terms of religion, afterlife, nature God, etc. should come up if you know somebody for a long enough period of time (that's my experience as a college student, anyway). As a Christian, and I speak primarily to those who are atheist, at what point do I cross the line from sharing my beliefs to being "pushy"? Is it a particular level of emotional arousal/intensity, a point at which I obstinately refuse to acknowledge your opinions - where would you start to feel uncomfortable?