“The last refuge of the insomniac is a sense of superiority to the sleeping world.”

April 7, 1775, p. 253
Boswell's full mention of this statement reads:
:Patriotism having become one of our topicks, Johnson suddenly uttered, in a strong determined tone, an apophthegm, at which many will start: "Patriotism is the last refuge of a scoundrel." But let it be considered, that he did not mean a real and generous love of our country, but that pretended patriotism which so many, in all ages and countries, have made a cloak of self-interest.
Life of Samuel Johnson (1791), Vol II

Phrases and Philosophies for the Use of the Young (1894)
Variant: Ambition is the last refuge of the failure
Context: Ambition is the last refuge of the failure.

"The Relation of Dress to Art," The Pall Mall Gazette http://www.gutenberg.org/files/14062/14062-h/14062-h.htm (February 28, 1885)
reprinted in Aristotle at Afternoon Tea:The Rare Oscar Wilde (1991)
Source: A Long Way Down

" O, Synecdoche, my Synecdoche! http://blogs.suntimes.com/ebert/2008/11/o_synecdoche_my_synecdoche.html," (10 November 2008)
Context: I was instructed long ago by a wise editor, "If you understand something you can explain it so that almost anyone can understand it. If you don't, you won't be able to understand your own explanation." That is why 90% of academic film theory is bullshit. Jargon is the last refuge of the scoundrel.

Source: City of Bones

Source: City of Bones

Variant: Sedate ignorance is the last stage of deterioration.
Source: Meditations in Wall Street (1940), p. 135

Source: Transformations

Variant: Violence is the last refuge of the incompetent.
Source: Part II, The Encyclopedists, section 5; This also appears three times in "Bridle and Saddle" which is titled "The Mayors" within Foundation. It is derived from the famous phrase by Samuel Johnson: "Patriotism is the last refuge of a scoundrel" and from the words of Lady Anne Bellamy in H. Rider Haggard's Dawn, “I do not believe in violence; it is the last resource of fools.” Asimov is usually quoted simply with "Violence is the last refuge of the incompetent."