There's really no substitute for a well-turned definition, so the following passage from a new writer at a new blog had me swooning:
Back when I took myself more seriously, I could not distinguish irreverence from arrogance or ignorance. They were all symptoms of the same shortcoming. But now, the lines are clear. Irreverence comes from complete honesty and respect. It’s the ability to step outside a serious situation, see it objectively, and help others understand it with levity. To throw down a much needed reality check just in the nick of time.
Influenced by the recent biographies of John Cheever and Donald Barthelme and the ingenious NCAA-like brackets of the Tournament of Books, said blog also features a nice showdown between the stories of Cheever and Barthelme.