„Prawdziwy przyjaciel zaatakuje cię od przodu.”

Oryginał

True friends stab you in the front

Also found in variants such as "A true friend stabs you in the front".
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 https://books.google.com/books?id=MF5-AAAAMAAJ&q=friend+%22stabs+you+in+the+front%22&dq=friend+%22stabs+you+in+the+front%22&hl=en&sa=X&ved=0ahUKEwig2JCRnKrMAhUC42MKHaNzCGsQ6AEIHDAA.
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 https://books.google.com/books?id=Xbe8zbfuVLgC&q=friend+%22stabs+you+in+the+front%22&dq=friend+%22stabs+you+in+the+front%22&hl=en&sa=X&ved=0ahUKEwjMjOrQnKrMAhVL2GMKHcQQDSgQ6AEIHTAA.
In 1984, an article in Ms. Magazine https://books.google.com/books?id=sfIbAQAAMAAJ&q=friend+%22stabs+you+in+the+front%22&dq=friend+%22stabs+you+in+the+front%22&hl=en&sa=X&ved=0ahUKEwjMjOrQnKrMAhVL2GMKHcQQDSgQ6AEIJzAC 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 https://books.google.com/books?id=CnQJAAAAIAAJ&q=friend+%22stabs+you+in+the+front%22+wilde&dq=friend+%22stabs+you+in+the+front%22+wilde&hl=en&sa=X&ved=0ahUKEwj2oqLfnKrMAhVG52MKHXdPANkQ6AEIJTAC: "A good friend is one who stabs you in the front". No source was given.
Disputed
Wariant: A good friend will always stab you in the front.
Źródło: e.g. "Broadway and Elsewhere" https://www.newspapers.com/newspage/3706522/, Pharos-Tribune (Logansport, IN), 1955-01-16, p. 4