I think you'll find you'll be sorely tempted to throw it! Because. I am offering. [He outright dramatically pauses.] To learn to make those greasy frisbees you like to eat. And. Then. To make them for dinner, for three days.

[Matching the bet in numbers and personal dislike of the task alike. He's not completely joking in encouraging Sans to throw the bet, for all he's not backing down. And as for the part where he's offering to eat these same burgers for three nights... Well, if he secretly runs the memory of the flavor of his ghost friend's gift, that's between him and whatever in his skull lets him taste things.]