An adaptation of a favorite book is almost always a colossal letdown. How can it compete with the version in your heart? Book-It's production of A Confederacy of Dunces is exceptional: It is absolutely, unbelievably anti-disappointing. Brandon Whitehead deserves a Nobel Prize for his embodiment of flatulent, grandiose grump Ignatius J. Reilly. The rest of the cast is just fantastic. Mary Machala, the director and scriptwriter, should be the patron saint of adapters. This is funny, funny stuff! You must go. (Center House Theatre, Seattle Center, 684-7200. 2 and 7:30 pm, $35. Through Oct 11.)