Have you thought about those phrases we use which mean the complete opposite to what they seem?
If you don’t mind me saying this... In other words, ‘I’m going to say this anyway, whether you like it or not.’
With all due respect… In other words, ‘No Respect At All.’
Even Thank you very much can sound very rude if said in a particular tone, as in. “I’ll let you know thank you very much.”
The American expression Have a nice day can, in some situations, means ‘Just go away. I don’t want to talk to you anymore.’
In addition, some words have adopted meanings which Dr Johnson, OED and all the other dictionaries never intended.
Sad – Outside what most teenagers do and wear. See also weird.
Cool – How teenagers would like to be.
Sick – Very much how teenagers would like to be.
Well ill – what other generations termed ‘sick’.
Also consider some common contemporary greetings. ‘You all right?’ ‘I’m good, yeah.’
If you write historical fiction, you carry out a lot of research, clothes, buildings, politics, social history… and how people speak. If you’re writing about a period in the distant past, you can’t use contemporary language in conversation, because the modern reader can’t cope with it, although you can pepper your dialogue with a few well-chosen period words. In Queen of the North by Anne O’Brien, set in turn of fourteenth and fifteen centuries, which I read recently, the characters spoke in modern idiom, with the odd late medieval word dropped in.
However, if you’re writing about the recent past, you can indulge in as much contemporary language as you like, but it’s difficult to remember what people were saying when… and where. Records of ways of speaking either don’t exist, are American or just don’t fit the situation you need. What all not-so-historical novelists require are records of what people said when, and where.
So here it is, then, my little record of modes of speech in England in 2019.