The verse (drum roll, please) is Omni 1:9. Here it is:
Now I, Chemish, write what few things I write, in the same book with my brother; for behold, I saw the last which he wrote, that he wrote it with his own hand; and he wrote it in the day that he delivered them unto me. And after this manner we keep the records, for it is according to the commandments of our fathers. And I make an end.This hilariously awkward attempt at writing by Chemish, who just didn't know what to do with the awesome responsibility of caring for the nearly filled record on the plates of Nephi, reminds me of what happens in so many talks at Church: "Well, when I saw the Bishop coming, I knew he was going to ask me to talk, and I told him I really didn't want to give a talk, but he said I should, and so I here I am. Anyway, now I'm giving a talk, and . . . is that two minutes yet?"
I think most of us can really relate to Chemish. Especially when we are young, giving a talk or writing an essay can result in a lot of silly words trying to fill up the space. Yes, Chemish shows that not every word in scripture is ponderous and spiritual - but we already knew that. It shows that real humans with real weaknesses sometimes were given responsibility over the sacred records. His words are just too funny, too natural, too human, and too "naturally out of sync" with the serious nature of the plates of Nephi for Joseph to have just made that up on the spur of the moment while dictating sacred scripture. If his purpose were to impress and deceive, this is the kind of thing you would not stick in the text. But this rough spot in the Book of Mormon shows the fingerprints of a real person, someone who might have been a bit rough around his spiritual edges but had to say something to fulfill the duty he inherited, thanks to his lineage.
Sure, chiasmus and Nahom and Bountiful and cement buildings are all interesting evidences for Book of Mormon authenticity - but what can beat Omni 1:9 as a "slam dunk" refutation of the theory that Joseph made up the Book of Mormon? OK, that's a slightly tongue-in-cheek statement, but perhaps only slightly.