Bon Buddhism is essentially the same as Zen Buddhism, except that it has nothing whatsoever to do with Buddhism.

Addendum I (November 23, 1989)

Bon Buddhism is to Zen Buddhism as I am to Gautama Siddhartha, who was not a Buddhist either.

Addendum II (December 8, 1989)

Bon Buddhism and Zen Buddhism differ mainly in practices relating to oral hygiene. According to Zen Buddhism, you should wash your mouth whenever you utter Buddha’s name. According to Bon Buddhism, you should wash your mouth twice whenever you utter my name, but there is no need to wash your mouth even once when you utter Buddha’s name.

Addendum III (April 9, 1990)

According to Annie Bloch, an old friend of mine from the Ph.D. Program at MIT who declares herself a Tibetan Buddhist, there is a branch of Buddhism in Tibet that is called Bön Buddhism. Although this is all I have learned from Annie, who materialized in my office at MIT for a brief afternoon after more than fifteen years of ethereal life in France, it is safe to conjecture that Bon Buddhism and Bön Buddhism differ only by an umlaut. Nevertheless, this is a significant difference.

Addendum IV (January 3, 1991)

Bon Buddhism is shit, just like Zen Buddhism.