Knackered
Exhausted.
Person 1"Coming out?"
Person 2"Can't, I'm knackered."
Where it's from
A knacker bought worn-out horses for slaughter, so a knackered horse was only fit for the knacker's yard. British in origin.

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While you're here
Extremely busy. Can be sarcastic about someone who isn't busy at all.
Extremely happy.
Get loud and rowdy, usually said of a party or a crowd. Also used for someone losing their temper.
Scare someone so badly they nearly wet themselves.
Extremely busy, with no hope of keeping up.
Completely exhausted or broken. Rooted means stuffed; gum trees have very deep roots.