A variation of a bear fight. The koala bear fight is performed by consuming a traditional bear fight (a Irish Car Bomb and a Jagerbomb consumed in rapid succession), followed by quickly drinking a can of Fosters.
Person 1: Hey mate, want to go get a round of koala bear fights?
When you're under influence of a drug and you get to places without knowing it was possible.
"I did a fair few shrooms and managed to climb a fat conker tree with no branches untill 3 metres up. Still no idea how that worked. Must have koala'd up there"