A mate of mine tried to pat a wild koala on the head. It did growl menacingly but didn't run off or bite him to be fair.
The Ausies call them "drop bears" as they drop from trees onto your back and gouge your eyes out with their formidable claws. As an aside they have two (clawed) thumbs as well as 2, maybe 3 "fingers". Mind you the Ausies also warn you about hoop snakes - which grab their tails in their mouths and roll down hills, hoop-like after you.