Bin / Dustbin: Trash can / garbage can.
Bog off: Go away.
Bollard: A little post to divert traffic on a road; a traffic cone.
Class-mark: The numbers on the side of a library book.
Climbing frame: A jungle gym.
Comprehensive: A school for children aged 11 to 16 or 18.
Do a bunk: Run away.
Estate: Several big apartment blocks— a housing project.
Git: Unpleasant person.
Knackered: Exhausted.
Lairy: Cheeky and aggressive.
Manky: Disgusting.
Minging: Dirty/smelly/unpleasant.
Mobile: Short for “mobile phone”— a cell phone.
Nutter: Somebody acting crazy.
Quite: When Americans say something is “quite good/bad/etc.,” you mean it is “very” good/bad/etc. When Brits say it, we sometimes mean it in just the same way— but then sometimes we mean something is only “fairly,” or “moderately,” or “kind-of-but-not-extremely” good/bad/etc. It can be confusing.
Rubbish: Trash / garbage.
Rum: Strange.
Sarky: Sarcastic.
Scrum: A confused situation involving lots of people.
Shtum: Silent.
Soft (“Don’t be soft”): Foolish.
Take the Michael: Mock, make fun of.
Tarmac: What they make airport runways out of, but we use it to describe normal roads, too.
Tower block: Big apartment block.
Yonks: A long time.