This sounds as silly a sibboleth as https://en.wikipedia.org/wiki/U_and_non-U_English ; I suggest we all start using 'delve' with wild abandon before these fools delve too greedily and too deep.

Maybe it's just because I'm American, but that chart toward the bottom seems all mixed up.

On the non-U side, there are fancy words like Knave, Looking Glass, Spectacles, Lavatory; but also non-fancy words like Die, Lunch, and what?.

On the U side, again there are both: Cemetary, Serviette, Pardon are all fancy; but Mirror, Glasses, Toilet are all non-fancy.

How old is that list, I wonder?

I'd also like to point out that Jam and Preserves are not the same thing, and usage of one over the other is not a matter of fanciness.

> How old is that list, I wonder?

1950s — and I'm pretty sure Miss Mitford was having everyone on.