Metaphor - Some folks think it's reasonable to prostelytize. Others find it offensive. Even milder evangelization can be quite annoying to someone who is not closed-minded, introspective, and does not need to be reminded to think about his beliefs.
Athiests are often inundated by believers who wish to just introduce them to the joy in their life. Here's a fairly un-subtle metaphor for that activity. But it is funny when you approach it this way.

Witness: Kissing Hank's Butt