Crackbrained

In order to ſet ſo hopeful a Genius right in this matter, vve have ſent you an anſvver to the ill-grounded Sophiſms of thoſe crack brain'd fellovvs, and likevviſe an eaſy mechanical explication of Perception or Thinking.

Source: wiktionary

By degrees, Jean Paul began to be considered not a strange, crackbrained mixture of enthusiast and buffoon, but a man of infinite humour, sensibility, force, and penetration.

Source: wiktionary

Could it be, after all, that the whole story was true, and the writing on the sherd was not a forgery, or the invention of some crack-brained, long-forgotten individual?

Source: wiktionary

He shook his head; the milk pail was still at his feet. «You always been a crackbrained sonofabitch anyhow.»

Source: wiktionary