A thin layer of corrosion or the protective coating is part of the fun...

Impress your friends with a huge shower of sparks, then hand it over upside down so your friends try to make sparks on the protective coating or a corroded part of the steel... Scraping the fire steel is the simplest action imaginable, but your friend will not succeed until he scrapes all the way down to unprotected material or realizes he needs to flip it over.

OK, just a sample of my bad taste in practical jokes, but there is a educative purpose here too. First you make a fool out of your friend, then show him the conditions for the sparks to fly. That lesson will stick.