bet dollars to doughnuts
bet you dollars to donuts
I assure you (that something will happen, with so much confidence that I would bet money against something less valuable). I lost my umbrella, so I bet you dollars to donuts that it rains tomorrow! Oh, I bet you dollars to donuts that Kevin will be late tonight—he's never on time!
bet someone dollars to doughnuts
Fig. to bet something of value against something worth considerably less. I bet you dollars to doughnuts that she is on time. He bet me dollars to doughnuts that it would snow today.