I don't think that's a UK thing, but rather just a close friends thing, which I experienced across multiple cultures. I recall a particular incident as a kid when my dad forcefully told me "Don't talk to me like that; I'm not your friend" and that stuck with me - you need to adapt your tone to the audience.
The last thing I expected was to get downvoted for just saying "English language can be a landmine if you are not careful, especially as a foreigner! lol".
English language uses words such as pussy that supposedly mean a cat, but at the same time they interpret it as vagina; another word is the name Dick which also is being used to mean phallus!
Meanwhile, I get downvoted for commenting the obvious thing which is, English language is absurdly confusing for me as a foreigner and have no idea what to say without offending every English speaker!