Smoking

What would happen if you smoked leaves off a tree ??

You'll probably get sick, depending on the leaves.
You're putting it into your lungs.

just dont smoke...its gross

This would largely depend on the tree. Some trees are harmless, others actually have toxins in them that would make you sick. Ever heard of poison oak? I am pretty sure most of them would not kill you, but nothing good can happen from it that is certain.

That would be incredibly stupid, regardless of what actually happened.

Go do it and find out