I was at a very posh dinner party earlier this week. At one point the guest on my right suddenly turned to me. “You know what I don’t understand,” he announced. “What’s a nice girl like you doing not being a Christian?” I was lost for words, at least any suitable for utterance at an ostensibly civilised gathering.

Then towards the end of the evening someone else caught sight of the heavily depredated cheese board and immediately thundered: “What utter reprobate has pointed the brie?” I didn’t know what pointing the brie meant (I just knew I wasn’t guilty, because I’d been too busy drinking myself quietly into a stupor) but eventually discovered that it means lopping off the tip of the communal wedge for your own use instead of cutting it lengthwise. I was also awed by the ease and clarity with which this guest had pointed out the social gaffe. If only I had found a similarly pithy put-down to the Christian interrogator.

It made me aware that we have an as yet unmet need for a set of agreed rules and dazzling bon mots for dealing with religious rather than circular-cheese-based matters. For those occasions when someone decides to ruin a perfectly serviceable conversation by interjecting religious nonsense. Of course we’d need a palette of put-downs, from the Dawkins-size sneer to the kindly, arm round the shoulder, my-dear-fellow-don’t-you-think-this-transubstantiation-stuff-is-the-teensiest-bit-silly mode for use with wayward friends.

I felt the lack of such a vocabulary the very next day when I found myself listening to a recently engaged friend, previously wholly unreligious, enthusing about the pre-marital “spiritual group sessions” he was attending at the home of the local vicar. He was finding it fascinating and fulfilling, he told me, offering the potential for “answering all those questions you have milling about in your brain but never get round to asking.”

He asked me what I thought of his endeavours and what I thought was this: Dave is an intelligent man, but under-educated. Like a lot of people, he was too immature at the time to knuckle down and take exams seriously at school, and he didn’t have the kind of parents who could insist that he did. So he ballsed them up and has been living with the consequences ever since. He works underpaid, overlong hours in jobs that neither do his intellect justice nor afford him the time or money to read the books he’s missed out on, which might have satisfied his need for intellectual sustenance.

Into this void has stepped the kindly local vicar. Now, at last, Dave has someone who can feed his curiosity, stimulate and lead him into debate and introduce him to new ideas and concepts in an intimate and supportive tutorial group. But the gap being filled has absolutely nothing to do with spirituality or the existence of God, and everything to do with an unfortunate set of exam timings. He reminded me of my grandma, a feverishly bright woman from a family which gave no quarter to the idea that she could go to university. At 18, she immersed herself in Catholicism, with all the fact-learning and mastery of doctrinal tenets that required – the nearest she could get to the academic stimulus she was denied.

But of course I didn’t say anything to Dave because it was impossible to do so politely. While you can rail about someone blunting the brie as pointedly as you like, you still have to be circumspect when launching an attack on someone’s spiritual life, even if you find it far more upsetting than any mere breach of dinner etiquette. I look forward to the day when civilised behaviour at table will include saying to any earnest zealot spouting superstitious piffle: “What utter reprobate taught you that?” and setting about them with a rancid, smelly, overripe chunk of Cambembert.