Partner's slang language

[oreo2020]

My partner was born in 1970s and grew up in London. I am an immigrant.
He's now in his 40s and fairly professional and still uses a lot of slang language that he grew up with intermittently with friends and colleagues, for example:

Jack diddly squat
Brown bread
Bird (talking of me)
Snuff it
You get me
Bump off

And similar...

He also says 'Valentimes' instead Valentine's although he spells it correctly!

I don't correct him as English is not my native language but I find it somewhat stuck in 1980s and do think a grown up man would have grown his vocabulary as he was building up his life and career.
But maybe it's more common than I think?

How are you meant to say liquorice? I've just asked everyone in my office, one of whom is genuinely quite posh, and we all say "lickerish".

@KirstenBlest

Not sure why the LOL. It is pretty neutral.

There is no such thing as a neutral accent. I suspect you mean your accent is quite RP. RP is still an accent. As an accent is may be regionally non-specific, but is still provides massive clues to the speakers likely upbringing, in common with all accents. It is no better, or worse, than any other accent. It just is.

To everyone who's asked:

liquorice

It's liquoriSS. Or used to be. Lots of attempts to classify posh or non-posh English. Most well-known is probably Nancy Mitford's U or Non-U.

Betjeman also wrote a poem about social-climber English, trying to be U but getting it wrong, like Hyacinth Bucket. 'Phone for the fish-knives, Norman ...'

Also nugget (S.E.London) for nougat - noo-gah.

It's hardly likely that in OP's country, people speak the same everywhere. Even on small islands, north to south speak and slang differently.

I learned English abroad. Arriving in UK I lived in East London. Went to grammar school but didn't speak "grammar" at home really, why bother? You're relaxed at home.

eg £5 is still a Jacks or a Bluey to me, if you ask me to sub you a Ton then I'll know the score, when chatting with mates from East. Obviously I don't speak like that at work.

Code Switching is a thing.