From what I can remember I think the closest any of them ever got was that they mentioned Christmas being a thing, but even that's more or less a regular holiday these days unless you actually include any of the religious bits (which I don't recall HP doing at all)
Everything said by the first person reeks of the usual "poor oppressed Christians" that evangelicals like to harp on about even though exactly none of them live anyplace where that's a thing.
☼ zinnia
: probably not, even though that is one of the few things Rowling did a good job at hammering in in the books, while failing incredibly at it in many ways in general herself.
So it's just super special to be presumably wanting to write fic/worldbuild for a fic in HP and decide "you know what! time to come up with a anti-religious-based reason for this slur!"