Ah yes. I forgot the ones who say that "religion doesn't matter" until AFTER you get serious with said theist, then it changes to, "I can't date/marry/live with someone who is not Christian/Catholic/Evangelical/Jewish/etc." So, you're faced with the choice of stopping seeing the person, complete with the hurt of the breakup, or at least pretending to convert to something which you do not believe.
I think this is particularly deceitful as a method of making converts! If the person didn't want someone who was not of their faith, they should have said so and declined in advance.
Then, there's always the family pressure to marry within one's own faith... or the faith of the family even if the person in question really is not particularly religious or privately disbelieves.

Then, there's always the family pressure to marry within one's own faith... or the faith of the family even if the person in question really is not particularly religious or privately disbelieves.