It reminds me of how people immediately get hostile in the presence of a Christian or someone otherwise religious.
People don't like being proselytized. I don't get hostile around Christians unless they come up to me with loaded questions like "so what Church do YOU go to" - and it's something every non or formerly religious person in the American South has to deal with and actually I don't usually get hostile, I ususally just leave. And honestly, it's such a rare occurrence that someone gets really bad about it, but when they do, it prejudices you against the next dozen religious folk you meet. :/
But I always throw hot dogs at the vegans - because the One True God appreciates the gesture.
