informal something that you say to emphasize that something is obviously not true.
He said the car in front backed into him, and if you believe that, you'll believe anything!
(redirected from If you believe that, you'll believe anything!)
if you believe that, you'll believe anything
That is obviously false. The phrase implies that if someone can't identify something that is so obviously untrue, they are apt to accept any falsehood. A: "My son said his teacher doesn't believe in grades, so they don't get report cards." B: "If you believe that, you'll believe anything!"