Crackpot
Crackpot was a derogatory term for an insane person.
In 2267, upon hearing his lawyer ramble on about books holding the law rather than computers, James T. Kirk commented, "You have to be either an obsessive crackpot who's escaped from his keeper or Samuel T. Cogley, attorney at law." Cogley confirmed both to be true. (TOS: "Court Martial")
In 2381, Brad Boimler called resident conspiracy theorist Steve Levy a crackpot with dangerous beliefs. (LD: "Caves")