Ridgy-didge
Genuine, the real thing.
Person 1"Is that an actual signed Bradman bat?"
Person 2"Ridgy-didge. Got the certificate and everything."
Where it's from
Rhyming play on ridge, old slang for gold or anything genuine. Same family as fair dinkum.

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While you're here
Genuine, true, no word of a lie. Also a question: "Fair dinkum?"
No. Starting with yeah makes it sound a bit more friendly.
Afternoon. Used heaps by basically everyone.
Petrol station. Also where you buy a pie, milk and a bag of ice at 11pm.
Toilet. Traditionally an outhouse down the back of the yard, now any toilet at all.
Used to explain something that's chaotic or a complete mess.