Paper (rectangle, not square)
Pencil (new and unsharpened)
Tape (duct tape recomended)
This is pretty simple and requires little origami knowledge.
Step 1: Step one
Step 2: Fold in half
Step 3: Step 3
A suggestion by a certain commenter says that you should crease everything as much as you can after this step. I'm sure it will work
Step 4: Step 4
Step 5: Kind of Complicated...
Step 6: Get it to look like the kunai
Step 7: It's gonna kill you!
Step 8: Putting it all together
Step 9: Have some fun... With tape!
Now you can put the pencil in the untaped end and wrap tape around the short end to tighten it and keep the pencil in.
Optional: wrap tape around the pencil (it matches)before you put it in the paper.