(1) The trademarked slogan of the General Mills breakfast cereal Wheaties, a product that has been marketed since 1924.
(2) The title of Kurt Vonnegut's 1973 novel Breakfast of Champions, or Goodbye Blue Monday.
(3) A ironically humorous expression that is used to indicate a food or beverage that isn't very good for you.
EXAMPLE of senses (1) and (2):
' The expression"Breakfast of Champions" is a registered trademark of General Mills, Inc., for use on a breakfast cereal product. The use of the identical expression as the title for this book is not intended to indicate an association with or sponsorship by General Mills, nor is it intended to disparage their fine products.'
-- Kurt Vonnegut, being ironical on page 1 of the Preface to his 1973 novel Breakfast of Champions, a tongue-in-cheek admonition he repeats verbatim in Chapter 18 (on page 195).
EXAMPLE of sense (3):
'Like everybody else in the cocktail lounge, he was softening his brain with alcohol. This was a substance produced by a tiny creature called yeast. Yeast organisms ate sugar and excreted alcohol. They killed themselves by destroying their own environment with yeast shit.
'Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne. . . .
' I now had Bonnie MacMahon, bring more yeast excrement to Beatrice Keedsler and Karabekian. Karabekian's drink was a Beefeater's dry martini with a twist of lemon peel, so Bonnie said to him, "Breakfast of Champions."
' "That's what you said when you brought me my first martini," said Karabekian.
' "I say that every time I give anybody a martini," said Bonnie.
' Doesn't that get tiresome?" said Karabekian. "Or maybe that's why people found cities in Godforsaken places like this -- so that they can make the same jokes over and over again, until the Bright Angel of Death stops their mouths with ashes."
"I just try to cheer people up," said Bonnie. "If that's a crime, I never heard about it till now. I'll stop saying it from now on. I beg your pardon. I did not mean to give offense."
. . . ' Her husband, meanwhile, was at home watching professional golfers on television, and getting smashed on yeast excrement.'
-- From Kurt Vonnegut's 1973 novel Breakfast of Champions, Chapter 19 (pages 208 - 211).
1973 KURT VONNEGUT, JR. Breakfast of Champions, or, Goodbye Blue Monday.