Streets ahead.

If you have to ask, you're streets behind.

https://www.merriam-webster.com/dictionary/nonplussed

A lot of people think it means unhappy, but it really means bewildered. Confusion over the definition has led to a new use as unimpressed.

"Clear as mud?"

Normally said after I tried to explain something and I'm only getting a blank stare in response. Or after a meeting when I know everyone is confused.

Ooh, another one I just remembered, translated from Afrikaans: 'Piggie war'.

Used to refer to a conflict where there are no winners, like pigs fighting in mud, where all participants just end up dirty, humiliated and bruised. Like replying to a troll online.

Much of a muchness.

Used to describe something redundant or superfluous. Naming a cat is much of a muchness; it won't come when you call it anyway.

That's not how you play cricket.

Used when someone or something is obviously bending or breaking the rules in an ungentlemanly manner. Capitalism is not how you play cricket.

Pussy on the chainwax!

As an answer to an obvious question:

"Does the pope shit in the woods?"

The answer is yes. Yes he does.

Do you ever listen to A Way with Words?

https://www.waywordradio.org/

Getting two birds stoned at once.

An old uni friend of mine from Northern Island made up a word for that thing when you drink in the afternoon and then stop for a bit and you get really tired: "Cafaggerhaggied"

It's sounds much better in a NI accent, though

Some slang from York, UK that was common in my childhood:

Pushknacker - a bicycle, particularly a street bike. Best one on this list, tbh, it's a great word.

Lagin - pronounced la-jin. Means rubbish. Like, "your pushknacker is lagin!"

Weeny - really, as in "that's weeny lagin"

Chava - pronounced char-va, a derogatory term, to be honest I never had any idea what the actual meaning was but it's an insult, as in "ya fuckin chava!". I was confused when the word "chav" suddenly became a thing years later and I've always wondered if they are related or if it's a coincidence.

Ding - what people would now call a chav, also used ad a general insult.

Dingraff - either the full for of ding, or an extension of it, no idea. General insult.

"Mallyhacked" - meaning something that is broken or destroyed. I heard this phrase a lot from older folks during my childhood, but never by anyone who wasn't from my area. My SO didn't believe it was a real word so I did some digging and I think that it is likely a very regionally accented version of "malahack".

Urban Dictionary says that malahack comes from the Lumbee-English slang of southern North Carolina. I don't think that's quite accurate because I'm not from anywhere close to North Carolina. My preferred reference is from The Vocabulary of East-Anglia: An Attempt to Record the Vulgar Tongue of the Twin Sister Counties Norfolk and Suffolk, as it Existed in the Last Twenty Years of the Eighteenth Century, and Still Exists: with Proof of Its Antiquity from Etymology and Authority; in Two Volumes · Volume 2 by Robert Forby, 1830:

Malahack, v. A word ludicrously fabricated, which means to cut or carve in an awkward and slovenly manner.

“Gong show”

Chaotic or poorly organized

The graduation ceremony was a total gong show, even the principal was drunk

Not a phrase but I’ve been saying the word “absolute” instead of “absolutely”. I’m a legend in my own mind.

Wide awake nightmare: A terrible thing you have to live with, you can't just wake up from it.

As in the line from the MST3k episode The Scream Skull, "This is Micky, Micky is a wide awake nightmare."

Aussie here. A classic bit of slang is "I'm not here to fuck spiders".

I also enjoy the word "nonosecond", which is the moment immediately after you realise you've fucked up.

"Gettin shitty", my buddy's personal phrase for getting drunk, probably hoisted from his dad.