A koala is sitting up a gumtree  

 smoking a joint when a little lizard walks past  and looks up and says
     

 "Hey   Koala !  what are you doing?"  

The koala says: "Smoking a joint, come up and have some."

So the little lizard climbs up and sits next to the koala and they have a few joints.

After a while the little lizard says his mouth is 'dry' and is going to get a drink from the river.

But the little lizard is so stoned that he leans too far over and falls into the river.

A crocodile sees this and swims over to the little lizard and helps him to the side, then asks the little  lizard: "What's the matter with you?"

The li ttle lizard explains to the crocodile that he was sitting smoking a joint with the koala in the tree, got too stoned and then fell into the river while taking a drink.

The crocodile says he has to check this out and walks into the rain forest, finds the tree where the koala is sitting finishing a joint, and he looks up and says "Hey you!"

So the koala looks down at him and says:
 
"Shiiiiiiiiiiit dude.......how much water did you drink?!!"