In Which I Despair

The following conversation took place at work today - I must admit I did not hear the beginning properly hence the blank bits but the 'fun' (?) part came later.

S: "...I've been asked to be a Godmother..."
M: "...christening..."
S: "...yes..."
M: " ...it won't be in a church cos they're not Christians."
Me: "sorry? They're not Christians?!"
S:.......
M: "They're not Christian, they're Catholics.
Me:"yeah, they're Christians"
M:*snottily* "It's not a christening, they're C a t h o l i c s so it won't be in a Christian church."
Me:"Call it baptism, christening - not all that different, really. Catholics are Christians!"
M: "No. Protestants are Christians."
Me: Are you joking?! Catholicism is built on Christianity. Their whole faith is based on Jesus Christ, Son of God. They're Christians."
M: "No. They're not Church of England
Bubbles: "OF COURSE THEY ARE CHRISTIANS! All of England used to be Catholic but it all changed when Henry VIII......."
M: "Oh"
Me: *muttering* "What the fuck did you think they were? So stupid."

I just can't believe it. Fair enough if you don't know the tiny details of each religion or faith but for fucks sake!!

UPDATE: I know I should let it go but there's one thing that's been bugging me. The stupid girl argued with me about something I studied at Uni and I taught it at high school (miss my students). I can't vouch for the quality of my teaching but I'd fucking D I E if my students failed to pinpoint Catholicism as a Christian faith. It really vexes me.