21 You may say to yourselves, “How can we know when a message has not been spoken by the Lord?” 22 If what a prophet proclaims in the name of the Lord does not take place or come true, that is a message the Lord has not spoken. That prophet has spoken presumptuously, so do not be alarmed.
Deuteronomy 18:21-22 | NIV
Mine would be all the failed prophecies. Time and time again they have been proven wrong in their predictions. They use the "light gets brighter" scripture out of context to explain their mistakes but by doing so they make their God a liar.