All things are forgetable but insults. (unatoned)
- Notebook #32, published in Pudd'nhead Wilson (2024)

He is dead and buried now, though; let him rest, let him rot. Let his vices be forgotten, but his virtues be remembered; it will not infringe much upon any man's time.
- "Reportorial," Territorial Enterprise, February 26, 1863 (mock obituary for the "Unreliable")

...he wasn't a very heavy weight, intellectually. His head was an hour-glass; it could stow an idea, but it had to do it a grain at a time, not the whole idea at once.
- A Connecticut Yankee in King Arthur's Court

Endowed with a stupidity which by the least little stretch would go around the globe four times and tie.
- Mark Twain in Eruption

A strange and vanity-devoured, detestable woman! I do not believe I could learn to like her except on a raft at sea with no other provisions in sight. [regarding Lilian Aldrich]
- dictation, 3 July 1908, Autobiography of Mark Twain, Vol. 3 (2015)

...knew all salt water learning, but in land matters didn't know as much as a dial in the dark.
- quoted in "Relics of Mark Twain," Boston Daily Globe, February 4, 1911, pg. 11 - a story on marginalia and separate notes found tucked in Mark Twain's personal library books

He would have been a black and tan terrier only there wasn't room enough on him for both colors.
- quoted in "Relics of Mark Twain," Boston Daily Globe, February 4, 1911, pg. 11 - a story on marginalia and notes found tucked in Mark Twain's personal library books

Of a much praised book by Henry James--once you put it down, you simply can't pick it up.
- quoted without source in Wit and Wisdom of Mark Twain, Alex Ayres-editor.
The quote has also been attributed to Mark Twain as a reaction to Jane Austen's work.