dollars and doughnuts
i’ll bet dollars to doughnuts he doesn’t know what he’s talking about
heard it before, never knew what it meant, until now.
Dollars to doughnuts means ‘most certain’ or ‘most assuredly’. It comes from the idea of betting. Betting a dollar to a half-dollar, for instance, means that you’re giving 2 to 1 odds–you’re willing to risk a dollar to win only a half-dollar. Being willing to bet dollars against doughnuts (viewed as worthless) means that you’re totally confident that you’re right, so confident that you’ll bet money against nothing.
The expression is also found in a number of variants, including dollars to buttons, dollars to dumplings, and dollars to cobwebs, each of these objects being considered worthless.
Dollars to doughnuts as an adjectival or adverbial phrase is first found in the late nineteenth century in America. The first explicit reference to betting is not found until the 1920s, in a story by “Ellery Queen”–“I’ll bet dollars to doughnuts Field played the stock market or the horses”–but betting is unquestionably the origin of the expression. (reference)
Clearly, this definition is inaccurate, as either Homer Simpson or myself could attest, donuts have infinitely greater value than their monetary counterparts, dollars.