The book has dozens of potential candidates. Sergeant Pluck's interpretation of the atomic theory in relation to bicycles is probably the most well-known.
In one of many touches of Black Comedy, the narrator's family's friends and acquaintances are so careful and euphemistic about the deaths of his parents that several years go by before he figures out that they are dead and he is an orphan. By the age of sixteen, at least, he has it pretty well sorted.
My mother was the first to go and I can remember a fat man with a red face and a black suit telling my father that there was no doubt where she was, that he could be as sure of that as he could of anything in this vale of tears. But he did not mention where and as I thought the whole thing was very private and that she might be back on Wednesday, I did not ask him where.