"The Late Benjamin Franklin", The Galaxy, Vol. 10, No. 1, July 1870 http://books.google.com/books?id=2TIZAAAAYAAJ&pg=PA139. Anthologized in Mark Twain's Sketches, New and Old‎ http://books.google.com/books?id=5LcIAAAAQAAJ (1875)

“…[H]eaven for climate, Hell for society.”

Mark Twain

Speech to the Acorn Society (1901)
also given as: "Heaven for climate, Hell for companionship." (unsourced)

“Ages of restriction to the one tool which the law was not able to take from him--his brain--have made that tool singularly competent…”

Mark Twain book Concerning the Jews

Concerning the Jews (Harper's Magazine, Sept. 1899)

“The 'bus is English. When that is said, all is said. As a rule, any English thing is nineteen times as strong and twenty-three times as heavy as it needs to be. The 'bus fills these requirements.”

Mark Twain

Source: Autobiography of Mark Twain, Volume 1 (2010), p. 111

“Compliments make me vain: & when I am vain, I am insolent & overbearing. It is a pity, too, because I love compliments. I love them even when they are not so. My child, I can live on a good compliment two weeks with nothing else to eat.”

Mark Twain

Letter to Gertrude Natkin, 2 March 1906 http://digitalcollections.nypl.org/items/53b4cf90-7739-0132-f12c-58d385a7b928

“Persons who think there is no such thing as luck—good or bad—are entitled to their opinion, although I think they ought to be shot for it.”

Mark Twain

Source: Autobiography of Mark Twain, Volume 1 (2010), p. 380

“Not a single right is indestructible: a new might can at any time abolish it, hence, man possesses not a single permanent right.
God is Might (and He is shifty, malicious, and uncertain).”

Mark Twain

Source: Mark Twain's Notebook (1935), p. 394.

“Formerly, if you killed a man, it was possible that you were insane—but now, if you, having friends and money, kill a man, it is evidence that you are a lunatic.”

Mark Twain

"A New Crime", first published as "The New Crime" in the Buffalo Express, 16 April 1870. Anthologized in Mark Twain's Sketches, New and Old‎ http://books.google.com/books?id=5LcIAAAAQAAJ (1875).

“The bicycle had what is called the 'wabbles', and had them very badly. In order to keep my position, a good many things were required of me, and in every instance the thing required was against nature. Against nature, but not against the laws of nature.”

Mark Twain

"Taming the Bicycle" (1917)

“Everybody yelled at him, and laughed at him, and sassed him, and he sassed back, and said he'd attend to them and lay them out in their regular turns, but he couldn't wait now, because he'd come to town to kill old Colonel Sherburn, and his motto was, "Meat first, and spoon vittles to top off on."”

Mark Twain book Adventures of Huckleberry Finn

Source: Adventures of Huckleberry Finn (1885), Ch. 21

“These facts are all on the credit side of the proposition that the Jew is a good and orderly citizen. Summed up, they certify that he is quiet, peaceable, industrious, unaddicted to high crimes and brutal dispositions; that his family life is commendable; that he is not a burden upon public charities; that he is not a beggar; that in benevolence he is above the reach of competition. These are the very quintessentials of good citizenship.”

Mark Twain book Concerning the Jews

Concerning the Jews (Harper's Magazine, Sept. 1899)

“Citizenship? We have none! In place of it we teach patriotism which Samuel Johnson said a hundred and forty or a hundred and fifty years ago was the last refuge of the scoundrel -- and I believe that he was right. I remember when I was a boy and I heard repeated time and time again the phrase, 'My country, right or wrong, my country!' How absolutely absurd is such an idea. How absolutely absurd to teach this idea to the youth of the country.”

Mark Twain

True Citizenship at the Children's Theater 1907