My oldest is allergic to Walnuts and Pecans - aka Tree Nuts. To be safe we avoid all foods with any trace of a Tree Nut (including almonds, hazelnuts, etc). I make sure his school knows, and there's even a sign outside his classroom declaring it a Tree Nut free zone.
I would be furious if someone did this to my child, and I find this article distrubing. However, what's even more distrubing were the comments. Many stated the child needed to stand up for themselves, how ridiculous to call a PBJ a deadly weapon, so on and so on.
What these ignorant individuals don't understand is that not everyone reacts the same - what will not cause an allergic reaction in one person may throw the other into full anaphlactic shock.
It is my belief that if the child in the story did go into anaphlactic shock from having peanut butter smeared on his forehead then the Bully should have been charged with attempted murder. It's no different then that child pointing a gun at someone and pulling the trigger to see what happens - it could have grazed the targeted individual or it could kill.