The Flexi-Pen is the writing utensil of choice in prisons because it can't be used to shiv someone. I bet it's fun to fidget with too. Amazon sells a five pack for $13.
The Flexi-Pen is made with a soft rubbery material that bends under the slightest pressure, making it nearly impossible to do lethal damage with it. It's as close to a stab-resistant, non-lethal weapon you can get, while still providing the subject with a workable ballpoint pen to write with.
It's ideal for use in interview rooms, holding cells, and in any prison or jail environment. You go to great lengths to confiscate any potential weapon when taking a prisoner into custody, so why would you want to hand him one afterward?