“Hey, check this weirdo out." Hi was inspecting a bust on the mantel. "This face is ninety percent eyebrow. What do you want to bet he owned slaves?"

Scowling to match the carving's expression, Hi spoke in a gravelly voice.”

Source: Attributed in posthumous publications, Einstein and the Poet (1983), p. 31
Spoken on hearing German marchers singing war songs. On p. 474 of Alice Calaprice's The Ultimate Quotable Einstein, she lists "we only use 10 percent of our brain" as a quote "misattributed to Einstein", perhaps this is the source of the misquote? Einstein seems to be speaking metaphorically here, not endorsing the myth http://www.snopes.com/science/stats/10percent.asp that science has shown 90 percent of the neurons in our brain lie dormant. And the myth dates back to before this interview, for example the book Mind Myths: Exploring Popular Assumptions About the Mind and Brain, edited by Sergio Della Salla, has a chapter by Barry L. Beyerstein titled "Whence Cometh the Myth that We Only Use 10% of our Brains?" which shows on p. 11 an advertisement from the 1929 World Almanac containing the line "There is NO LIMIT to what the human brain can accomplish. Scientists and psychologists tell us we use only about TEN PER CENT of our brain power."
Context: What a betrayal of man's dignity. He uses the highest gift, his mind, only ten percent, and his emotions and instincts ninety percent.

"The other ten percent."
Clary and Jace, pg. 83-4
The Mortal Instruments, City of Bones (2007)

Travis McGee series, Dress Her in Indigo (1969)
Context: Any man who outgrows the myths of childhood is ninety-nine percent aware and convinced of his own mortality. But then comes the chilly breath on the nape of the neck, a stirring of the air by the wings of the bleak angel. When a man becomes one hundred percent certain of his inevitable death, he gets The Look.

Source: Saving Francesca

Quote in Maillol's letter, 14th May 1887; as cited in Renoir – his life and work, Francois Fosca, Book Club Associates /Thames and Hudson Ltd, London 1975, p. 245-246

Source: They'd Rather Be Right (1954), p. 175.

Source: Don Quixote de la Mancha (1605–1615), Part I, Book I, Ch. 4.