1. He came up with a crackbrained idea to solve the problem, but nobody took it seriously.
他提出了一个疯狂的主意来解决问题，但是没有人把它当真。
2. Don't listen to his crackbrained theories, they are completely illogical.
别听他那些愚蠢的理论，它们完全没有逻辑。