Just recently I was in a conversation with a number of UK mainlanders and we had a debate over what "tories" meant, apparently disproportionately ordinarily it refers to a political party and it's not usual to use it as short for "territories" as I've used it (according to how the debate ended, it was half and half between them). And once again I'm reminded of how people feel to look back at their usage of a word/phrase over the years and cringe.
More tragically, me and a friend were embarrassed once upon realizing everyone was confusing "encephalitis" with "hydrocephalus" when talking to someone about their kid with hydrocephalus. Awkward because encephalitis is caused by HIV.
Since OP is in the UK, I can pull out “nonplussed.” Current American usage of the word is a lack of surprise or general acceptance. I am nonplussed when news arrives that another politician was caught in a sex scandal. Non-American usage is complete surprise and an inability to act. The Scot was nonplussed when the drunk American vomited noisily on his shoes.
Edit: I am firmly in the “general acceptance” camp and usually have to process for a second or two when someone uses it in its traditional sense.
Not in the UK itself (hence I distinguish them with "mainlanders"), just someone who has lived a commonwealth/territorial upbringing and has moved around a few times. The debate with said mainlanders sticks out because people within the physical UK differ largely in how they say things, and when you emulate them and fail from the perspective of someone from a lesser part of the anglosphere, you can't make the case as well that it's just a matter of different equally valid uses for the same vocabulary.
Ahhhhhh good clarification! Sorry for missing the location point.