pieman; here it is, credit to Martha Barnette and http://funwords.com

dollars to doughnuts


Most assuredly; with certainty.

You usually hear this idiom used in the phrase as "I'll bet you dollars to doughnuts that . . ."
But why doughnuts?

The idea behind this phrase is the bettor is so certain of being correct that he or she is willing
to risk something valuable (i.e., dollars) against something virtually worthless. In the past, the
same idea has been expressed in the phrases dollars to cobwebs and dollars to buttons. But,
perhaps because of its deliciously alliterative quality, dollars to doughuts" eventually won
out.

"Oh, I'll bet you dollars to doughnuts those aren't real!"

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