It's such a beautiful day that Phineas and Ferb decide that today is a good day to do nothing. Candace, not knowing what to do when Phineas and Ferb aren't doing anything bustable, tries to get them to do something. Meanwhile, Dr. Doofenshmirtz has created the Ugly-Inator, a device that will render anything and anyone ugly, making Doofenshmirtz handsome by comparison. Perry tries to stop him, but Doofenshmirtz has invented another device, the Slow-Motion-Inator, slowing Perry to the point where he is unable to catch up with Doofenshmirtz.
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!Tropes:
* FiveFiveFive: The number to call to order the Man Eating, Dinosaur Themed, Totally Sick Waterslide of Doom is 555-0100.
* AbortedArc: Phineas and Ferb wake up prepared to make a railroad in the backyard, but as soon as they see how nice a day it is, they decide to just do nothing all day.
* ArtistAndTheBand: Jeremy and the Incidentals. Also somewhat of an inside joke since the other members of Jeremy's band are background characters.
* BatmanGambit: Candace attempts to build an amusement park ride by herself in order to get Phineas and Ferb to do it instead so she can bust them. It doesn't work and she ends up almost missing Jeremy's concert because of it.
* BorrowedCatchphrase:
-->'''Delivery Guy:''' Aren't you a little old to be building one of these things?\\
'''Candace:''' Why yes, yes I am.
* DisabilityImmunity: When Perry fires the Ugly-inator at Doofenshmirtz, it does nothing to him, because he is already ugly.
-->'''Doofenshmirtz:''' Oh no, now I'm ugly- [notices that he's unchanged] Oh, oh I get it. Hardy-har-har.
* EarlyBirdCameo: The music heard when Monogram and Carl dance and when Agent P chases Doofenshmirtz would later be used for "Platypus Walk".
* ExactlyWhatIAimedAt: Doofenshmirtz notices Perry (in slow-mo mode) attempting to steal the Ugly-inator, which he then takes away and runs off with, mocking Perry for being too slow to catch him. Turns out Perry is trying to get to the Slow-Motion-Inator instead to reverse its effects.
* ExistentialHorror: PlayedForLaughs. Since Phineas and Ferb decide to do nothing, Candace has no one to bust, throwing off her routine.
-->'''Candace''': You can't do anything unless you're trying to bust them for doing something! And if they're doing nothing then... who... is... Candace?
* FailureIsTheOnlyOption: No matter what Candace does, the boys won't do anything on their do nothing day.
* FantasySequence: When Candace sees her brothers just standing like statues, she has a thought bubble about her brothers putting up decoys in order to drive her crazy.
* InconvenientSummons: When Perry enters his lair, Monogram and Carl are onscreen at a dance club with a couple of girls. When Monogram notices Agent P, he tells Carl to give him a close up and says, "So anyway... Stop Doofenshmirtz. Hit it, Carl!" and the dance resumes.
* ItsTheBestWhateverEver: The title of the episode itself. Also the TitleDrop at the end.
* PunishedWithUgly: Inverted. Perry fires the Ugly-inator, now fueled with a beautiful photo of actor Vance Ward, to turn Doofenshmirtz's hot air balloon into a beautiful one with "I Love Goodness" written on it, much to Doof's chagrin.
* RapidFireDescriptors: "The Man Eating, Dinosaur Themed, Totally Sick Waterslide [[DoomyDoomsOfDoom of Doom]]!"
* RecordNeedleScratch: When Perry drops in to O.W.C.A. headquarters, Major Monogram and Carl are having a dance party with two women; when they realize that Perry's in the room, we hear a record scratch and Monogram tells Carl to cut to closeup.
-->'''Major Monogram''': So, uh... anyway... stop Doofenshmirtz! Hit it, Carl!
* SanitySlippage: This episode essentially crosses "Driving our sister insane" off the list in the title sequence.
* SlowMotionFall: Perry uses the Slow-Motion-inator to slow down his fall with Handsome Movie Actor Vance Ward.
* SpecialGuest: Creator/DiedrichBader (who would later go on to voice Albert) voices handsome movie actor Vance Ward.
* TakeThat: Doof’s Ugly-inator turns Jeremy and his band into a grunge band and the audience into goths.
** It also turns a recliner into a deckchair.
* ThatCloudLooksLike: In one of the lyrics of Jeremy's song in the episode's credits:
-->''The clouds look like sheep and vice versa, on a do nothing day''
* ThrowTheDogABone: The day ends for Candace with her and Stacy joining Jermey’s band on a stage, as she and Jermey sing a duet together.
* TitleDrop: Done by Phineas near the end after Mom comes home.
-->'''Linda:''' Oh, I see you're still enjoying your do nothing day.\\
'''Phineas:''' Yeah, Mom. It was the best lazy day ever.
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->''[[TheStinger This is the best day ever!]]''