In Firefly Ep. 8: Out of Gas, Wash walks into the dining room in the middle of Shepherd Book telling a story about his life at the monastery:
ZOE: That is not true! No.
BOOK: I swear it is.
INARA: Surely one of you must have told him.
BOOK: No! Not one of the brethren had the heart to say anything. He was so proud.
WASH: [walking into the room] Of what? What was he proud of? Who he?
BOOK: Looked rather natty, truth be told, you know.
WASH: What was natty? I wanna hear about the natty thing.
KAYLEE: Shepherd Book was just tellin' us funny stories about his life at the monastery.
WASH: Monastic humor. I miss out on all the fun.
They never explain what's so funny! I sympathize with Wash, feeling left out while everyone else is laughing.
Is the story ever explained anywhere? Writer interviews? DVD commentary?