Not to give anybody ideas, but a pencil or pen can most definitely be a deadly weapon.
Place pencil over the subject’s eye, hit the eraser really hard with the heel of your hand or some heavy object.
It’s what I was going to try if hijacked after 9/11.
Only challenge is that your subject is not likely to hold still while you get set up. :)
That’s why you just stab them in the neck or under the chin, to incapacitate enough to give you the upper hand.
They don't have to be holding still if you can jab the point between their ribs and puncture a lung (or two). :=) While it may not kill them as quickly, it'll definitely take the fight out of them. (Just be sure to hold the pencil with the eraser in front of your pinky finger so that it doesn't slip through your fingers.)
They slow down substantially when you drive the bones in their nose into their brain. Course after that the pencil through the eye isn't STRICTLY necessary.