It's hard (maybe impossible?) for someone to descend lower than the class of their parents as upbringing is so important, though their
own children may one day be considered of the lower class, due to probably not being brought up in the same environment or having the same opportunities. Although Upper Class people don't tend to be as subject to this as other classes are.
WCs: 'toilet' is Middle Class and lower (definitely not Upper Middle), 'loo' or 'lavatory' is solid Middle, 'bogs', 'khazis' and 'traps' are Working though popular words with young men of all classes, 'heads' is Upper. 'Bathroom' will get you puzzled looks from everyone.
Gnomes: Working Class all the way, though those who've clawed into the Lower Middle (see Gerald in
The Full Monty) might still have them. Other classes only have them as 'ironic statements'.
Napkin Rings: the downfall of many would-be social climbers, these are only used by Lower Middles who have climbed from Working and actively want to go higher, but alas, using them reveals their social status, as nobody in higher classes would ever use them. In fact, the whole business of having or attending a dinner party is best avoided
entirely in Britain as it offers
so much potential for committing social faux pas.
This is part of why I love the start of The Hobbit and Lord of the Rings so much, as they are filled with cringeworthy moments and social awkwardness.