The Everywhere Sharpener

You're out somewhere, your knife is a bit dull from use, and you need to bring the edge back.  But for some reason you don't have any of your usual equipment for this.  What to do, what to do...

Find a coffee cup or mug, and flip it over.



The ring on the bottom that actually contacts the table (the saucer if you're fancy) is not glazed, so the bare ceramic is exposed.  That ceramic is quite abrasive, and you can use that ring to sharpen your blade.

I deliberately dulled this knife to the point it wouldn't cut anything (including paper) cleanly, and it took about a minute of strokes with light pressure on this mug ring to bring it back to a quite usable edge.

Note that it might upset the waitress at a cafe if you start using your coffee cup for this, so keep that in mind.