If you haven't realized yet, pencil sharpeners all have razors that can be removed and cause quite some damage.

Some rulers have a metal strip. A METAL STRIP! As if you seriously need that metal strip to draw better lines. More likely than not, it will mess up your lines. Getting wacked on the head with a wooden object would hurt, but once you add a metal strip you'll most likely see blood.

Then there is a large a.s.sortment of objects that can be brought to school without getting into trouble like screwdrivers and bricks (n.o.body would question it if you said it was for art cla.s.s).