Yes and no

Ways to agree and refuse, including yeah nah, which means no, and nah yeah, which means yes.

Bloody oath

Absolutely. Strong agreement.

"Bloody oath they will."

Does a koala shit in a gum tree?

Yes, obviously. The Australian answer to "Does a bear shit in the woods?"

"Does a koala shit in a gum tree and wipe his arse on a cockatoo?"

Get stuffed

Go away, and the answer is no. Strength depends entirely on tone; can be affectionate between mates.

"Get stuffed."

Keen

Up for something. "Keen?" on its own asks if you want to come.

"Heading to the beach. Keen?"

Nah yeah

Yes. Starting with nah brushes off any doubt before agreeing.

"Nah yeah, it was good."

No wucking furries

No fucking worries. A spoonerism of the stronger version of "no worries".

"No wucking furries."

Pig's arse

No way. I don't believe you.

"Pig's arse he did."

Sweet as

Great, or no problem. The "as" ends the sentence on purpose.

"Sweet as."

Too easy

No problem. Said when you agree to do something, or when someone thanks you.

"Too easy."

Yeah nah

No. Starting with yeah makes it sound a bit more friendly.

"Yeah nah, I reckon we give it a miss."