Get Smart (1965)

Season 1: Episode 8

Smart is to testify against KAOS soon, so they devise situations to show that Smart is losing his mind. A dying cowboy comes to Max's apartment to reveal a plot to poison the Morovian Ambassador at a costume party that night. Max calls the Chief, but when help arrives, the dead cowboy is missing and there's no proof of his ever having existed. Max dresses as a giant chicken and attends the costume ball at the embassy in order to protect the ambassador, but it's not a costume party and there's no poison in the ambassador's drink. It's all a KAOS plot to convince everyone that Max is crazy and discredit his testimony in an upcoming court case.