In a recent three-and-a-half-hour video homage to John Conway, one of the participants, Siobhan Roberts, recalls Conway telling her that "time flies like an arrow; fruit flies like a banana." Roberts has written a biography of Conway. Of all the stories she might have used to illustrate the man's wit, this one struck me as odd — since of course the quote wasn't a Conway original.
Sometimes attributed to Groucho Marx, quote investigator "Garson O'Toole" (Gregory F. Sullivan) got it right in 2010 when he traced the core of the quotation to Anthony Oettinger, quoting from Oettinger's September 1966 Scientific American article touching on the subject of grammar by computer (time flies vs. fruit flies; the complication is mentioned as early as 1963 in the Harvard Alumni Bulletin). O'Toole: "By 1982 or before someone juxtaposed the sentences to yield a funny combination which was then assigned to Groucho Marx."
The April 1975 issue of Computers and People already had the juxtapositioning. Lawrence M. Clark wrote "Computer Programs that Understand Ordinary Natural Language" (pages 14-19, 23; page 14 reproduced here, quotation boxed in green). It gets better. Clark's three sentences appeared already in the November 1966 issue of Computers and Automation (different title, same publication). Neil Macdonald (a pseudonym for Edmund Berkeley) wrote a short "Research on Meaning in Programming Languages" (page 10, reproduced here). It is "peach" instead of "banana" but that is not as important as the date.