Get Smart (1965)

S1E8 The Day Smart Turned Chicken

With Max about to testify against KAOS, they concoct scenarios to make him appear mentally unstable. One day, a dying cowboy visits Max’s apartment, warning him of a scheme to poison the Morovian Ambassador at a costume ball that evening. Max contacts the Chief, but by the time help arrives, the cowboy has vanished without a trace. To safeguard the ambassador, Max dons a giant chicken costume for the event, only to discover it's not a themed party and the ambassador's drink is safe. This was all a KAOS ruse to undermine Max's credibility before the trial.