Okay so after making a somewhat successful Skip (with continued thanks to Reject!), I'd like to present a couple of ideas.
1) A Sharp Blade: A 12 cm long blade, double edged, with two points and no handle. Simply put, it cuts through everything. Sounds horrifically stupid, no? Here's the catch: the atoms that the object is made up of are thousands of times smaller than any the atoms of any other element. Ergo, this makes it remarkably easy for it to split an atom, with virtually no kinetic energy from its neutrons. I might not understand science as well as I think I do. Please inform me if I'm a complete idiot in the realms of nuclear fission.
2) Ulcer Disease: Basically, a disease that slowly covers you, inside and out, with ulcers. However, this disease is not lethal an will force the body to maintain homeostasis.
3) The Dancing Man: A humanoid who is unable to move unless presented with recorded music. However, different types of music may affect his movement in different, sometimes dangerous or horrifying ways.
Please inform me if any of these are really stupid.