The title and introductory music are inspired by the 1942 film Yankee Doodle Dandy, a major hit and another Warner release. Other than the fact of both films being "about show business", they have no plot elements in common.
Daffy Duck, agent to the stars, complete with business card that flashes like a theater marquis, does everything he can to convince Porky Pig of "Smeller Productions" that his preadolescent client "Sleepy LaGoon" can become a star. This annoys Porky, as it is his day off and he has planned to play golf.
Daffy spends most of the cartoon telling Porky about what his client can do, while actually performing various schticks himself, in his usual wild and frenetic way. After trying various ways to escape, Porky locks Daffy in a huge vault and takes off in a plane, only to find out that the pilot of the plane was Daffy. Porky then jumps out with a parachute while Daffy follows. Porky then gets chased back to his office. Finally, Porky relents and asks to see what his client can do. "Sleepy", a small and droopy-eyed duck who has whiled away the episode slurping a huge all-day sucker which he keeps in a banjo case, finally gets to perform. "Sleepy" begins to sing a song in a strong baritone voice. He starts out well, then tries to hit a high note, and goes into a coughing fit as the cartoon ends.
The Warner cartoonists were known for occasionally playing jokes on themselves and their audience, sometimes "testing the waters" to see what they could get away with. In this case, during Daffy's Carmen Miranda impersonation, and out of character with the rest of the set-piece, a single frame appears to show Daffy subtly giving "the bird" to the viewer while grinning devilishly. This would have been invisible to the theater audience, but can easily be found with now-routinely available equipment that allows frame-by-frame study of films. Viewing a cartoon that way can reveal the amazing artistry of the Warner Studios. As well as revealing these amusing "easter eggs".
The sequence where Daffy performs "I'm Just Wild About Harry", a song more customarily sung by female vocalists, contains an arguable acknowledgement of homosexuality. When Daffy reaches the lyrics "The heavenly blisses / Of his kisses / Fill me with ecsta---" he stops abruptly to make sure Porky knows, "This is just a rough idea, y'understand," before completing the song.
Yankee Doodle Daffy is parodied in the South Park episode The Passion of the Jew, when Stan and Kenny are trying to escape Mel Gibson's house, a reference to Porky trying to escape from Daffy.
Yankee Doodle Daffy is twice referenced in the T.V. series SpongeBob SquarePants. First in the episode Rodeo Daze, where Sandy is seen riding SpongeBob like a horse, a possible reference to Daffy riding Porky like a horse. Secondly, in the episode Spongbob Meets the Strangler when the Tattletale Strangler tries to escape SpongeBob by jumping off of a plane and using a parachute, only to find that SpongeBob was the parachute, a gag borrowed from this cartoon.