and the moon is made of (green) cheese

Used to highlight one's utter disbelief or incredulity about something that someone else has said or believes. Often said alongside other things that are obviously false. A: "Tom claims he's descended from Napoleon Bonaparte." B: "Ha, yeah right, and the moon is made of cheese." A: "How can you say that? The governor has done an amazing job during this crisis!" B: "Sure, and the moon is made of green cheese, two plus two equals five, and the earth is flat!" You really think you've got a chance at this promotion after insulting the boss? Right, and the moon is made of green cheese.

moon (is) made of green cheese, (and) the

The most ridiculous thing imaginable. This farfetched figure of speech dates from the early sixteenth century. Despite the opinion of one collector of proverbs, F. E. Hulme (Proverb Lore, 1902), who believed it referred to the newness (“greenness”) of the moon each month, it has always been used as an example of outrageous absurdity.