when he tried to informally address Brigham in an official meeting (Twain's older brother was appointed to be the territorial governor of Nevada & they paid respects to Brigham as they were passing through SLC on their trek to the west). Knowing Twain, he was probably making a joke or something.

I think Twain was in his 20s at the time. Another thing: He & his brother were living in Keochuk Iowa just across the river from Nauvoo — before they made their trek to Nevada. And for some reason I don't think Twain ever points that coincidence out in the course of the travel book — even though he has a LOT to say about them Mormons (including an interesting chapter entirely on the Bk of Mormon — which includes the quip that it'd be the "pamphlet of Mormon" if the "it came to passes" were removed). He did have some positive things to say about the Bk of Mormon too, though.