Daffy Doodles is a Warner Bros. cartoon featuring Daffy Duck and Porky Pig. Daffy is the notorious "mustache fiend", bent on putting a mustache on every lip in sight, while Porky is a policeman intent on capturing Daffy.
Porky is then introduced as a policeman, set as a "booby trap" — he's holding up a picture frame around his own face. Daffy passes by, trying to get Porky to break his 'pose'. He then puts a box in front of Porky labeled "Do not open until Xmas" and walks off. Porky notes that he won't be around for Christmas, so he opens the lid to take a peek. Daffy jumps out, drawing a mustache on Porky's face and runs off, leaving Porky with the realization that Daffy's the mustache fiend.
To the tune of 42nd Street, Daffy goes to a subway platform, and holds up a paintbrush to the incoming train, giving everyone on board a mustache. As he's about to leave, Daffy is stopped by Porky who chases after him. Daffy then acts as a conductor, holding the doors open for Porky and telling him to "Push in!" Porky jumps on the train, and just before it pulls out, Daffy gives him another painted mustache.
Porky is now searching the streets, where he notices the various movie posters all defaced with a mustache (including posters for some Warner Bros. stars such as Peter Lorre, Humphrey Bogart... and even Bugs Bunny!). Meanwhile, Daffy comes across a giant billboard on top of a large building featuring a woman's face. Most predictably, Daffy is unable to resist, saying that "it'll be... my masterpiece!".
Porky, having come across more of Daffy's work (including a baby in a stroller with "Wet Paint" written on the side), sees something on the building in front of him. Looking through a telescope, he sees Daffy, a rope around his waist, painting a giant mustache on the billboard face. Porky gives chase and gets up to the billboard as Daffy is singing "She was an acrobat's daughter" while still swinging from the rope. Porky clubs Daffy in the head, and Daffy wanders to the edge. As Porky approaches, Daffy warns Porky "One more step, and I'll jump!" Porky takes another step, Daffy jumps — but when Porky rushes to the edge, Daffy is on a ledge, painting yet another mustache on Porky's face.
Porky then chases Daffy around the ledge of the building (Daffy even once saving Porky from falling), then is chased by Daffy on a motorcycle. The chase ends back on the roof, where both of them crash through a skylight and Daffy again wanders off (Porky, noticeably, has a 'mustache' from the motorcycle's handlebar on his face). Porky chases Daffy through the building, getting three more mustaches painted on his face (twice with a stencil, once where Daffy paints a mustache in mid-air and Porky runs into it).
Porky then spots Daffy inside a mail chute and races downstairs to pull him out. Daffy then slaps handcuffs on himself and Porky, saying "Wait'll J. Edgar Whoozis hears of this!". However, Daffy's mania gets the better of him again and he draws another mustache on Porky's face, but this time, he is clubbed by Porky while still handcuffed to him.
Daffy then faces a dog judge and asks for mercy, not to be sent to "Sing Sing...Sing...Sing", adding "You might be a fiend yourself someday." The judge turns to the jury and asks for their opinion. The jury — all composed of moustached Jerry Colonnas — tell the judge "Ah, yes! Not guilty!" Daffy then swears never again to draw another mustache — "I'm doing beards now!" He then proceeds to draw a beard on the judge and draws 'paint' over the screen until it's all black.