Notes from Wikiquote
The earliest known example of this quote comes from Walter Winchell's syndicated newspaper column in mid-January 1955: 'On Broadway, cynically reports Jimmy Nelson, "a true friend is one who stabs you in the front"' | The earliest version of this quote found in Google Books is from 1958, where the quote "A true friend is one who stabs you in the front" is attributed to actor Steve Dunne. | In 1981, a similar quote: "He is a fine friend. He stabs you in the front" was attributed to Hollywood writer and producer Leonard Levinson. | In 1984, an article in Ms. Magazine stated that "the Hollywood definition of a friend" was "someone who stabs you in the front". | The earliest attribution to Oscar Wilde was from 1989: "A good friend is one who stabs you in the front". No source was given.