People who have seen the anime Bakemonogatari will remember a certain character named Hitagi Senjouahara who uses regular stationary as deadly weapons.

In the anime, Hitagi has been seen either carrying or using items like pens, pencils, protractors, rulers, box cutters, scissors, and of course her favourite weapon: the stapler. That’s pretty much everything you would expect a student to use in school, but there is one very common item that Hitagi never uses: the eraser.

The reason why Hitagi never uses the eraser has, however, been answered in the comic below. Note thatsince this is Japanese, the panels are read from top right to bottom left.

The girl is Hitagi Senjougahara, and the guy is Koyomi Arargi.

Translation (via AnimeSuki Forums):

First frame
Hitagi: Araragi-kun. What might that thing you are holding be?

Second frame
Koyomi: This? It’s a Kadokeshi (brand of eraser)…

Third frame
Hitagi: I see, that’s what it is… this is the first time I’ve seen one being used in real life.
Koyomi: Really? I didn’t think Kadokeshi were rare or anything. For that matter, this is rather unexpected.
Hitagi: What is?

Fourth frame
Koyomi: My impression of you was that if it had to do with stationery you’d know everything. I thought you’d be just as familiar with erasers.
Hitagi: I’m afraid that I have no interest in erasers.

Fifth frame
Hitagi: After all, erasers don’t have any killing or wounding potential at all.
Koyomi: Senjougahara… you’re not supposed to select stationery based on their wounding potential.

Only in anime/manga would you find characters that choose what stationary she uses regularly based on wounding potential, but I would have to disagree that an eraser doesn’t have any. I’m sure that if you had very good aim, you could poke someone’s eye out with one.