After getting busted on a DWI ("driving while intoxicated," not DOA ["dead on arrival"], as Chief Wiggum learned) charge[[note]]even though he passed the road test before Barney told the cops to give him a Breathylizer test, and Barney was never arrested either, since he drank even more than Homer did[[/note]] after sneaking out of work to go to a Duff Beer Factory tour, Marge urges Homer to go 30 days without beer. Meanwhile, Bart destroys Lisa's steroid-injected tomato and becomes an unwitting test subject in her new science fair project: "Is My Brother Dumber Than a Hamster?"

!!Tropes featured:

* ActorAllusion: Lisa says she was chuckling over a joke from ''HermansHead''. Yeardley Smith was an actress on that show as well (even though she and fellow ''Simpsons'' voice actor HankAzaria don't like to acknowledge that they were on ''Herman's Head'').
* BedtimeBrainwashing: The episode opens with Principal Skinner awarding Bart first prize at the school science fair. The phrase "first prize" echoes until the scene transitions to reveal that Lisa was saying this into Bart's ear while he was dreaming because she was "just screwing with [his] mind."
* BrokenAesop: Invoked in-universe. An ad outside the Duff brewery says: "Friends don't let friends drive drunk" before it switches to a Duff ad depicting two friends drinking beer on the hood of a car.
* ComicBookTime: Ned says it's been 4,000 days since his last drink. 4,000 days is almost 11 years, but Ned makes it sound like his [[FelonyMisdemeanor bad event]] that made him join Alcoholics Anonymous only happened yesterday.
* CutenessProximity: Bart exploits this with his "Can hamster's fly planes" project. No one questions how relevant or scientific is because hamsters flying planes.
* DeadBabyComedy: Chief Wiggum confusing DWI with DOA. Also Homer laughing at the montage of car wrecks (and Troy [=McClure's=] attempts to make jokes during it).
* FairWeatherFriend: Homer goes back to Moe's who is happy to welcome him despite badmouthing him the day before.
* KarmaHoudini: Barney gets away with essentially kicking off the episode's main plot by urging the police to give Homer a breathalyzer test right after he flawlessly passed a field sobriety test (granted, Homer beat Barney pretty bad in order to dissuade him from driving). After failing the breathalyzer test, the clearly sober-enough-to-drive Homer is arrested, stripped of his driver's license, forced to attend AA meetings, and gets into a bet in which he can't drink beer for a month; meanwhile, the obviously skunk-drunk Barney is allowed to drive off, even knocking one of the cops off a cliff as he speeds away.
** Bart suffers no punishment for destroying Lisa's science fair project. When Lisa actually attempts to make him suffer some form of retribution, he responds by ''winning the science fair!''
** YMMV. What Bart did was bad but Lisa's retribution was pretty mean spirited (it basically boils down to her embarrassing him in front of the entire school). Neither kid comes off as the clear "good guy" in the episode.
* LaserGuidedKarma: Wiggum arrests the still relatively sober Homer, and allows the very clearly drunk Barney to drive home without doing any tests on him. He's immediately knocked off the road by Barney and sent rolling into a tree before [[StuffBlowingUp inexplicably blowing up]].
* LeaningOnTheFourthWall: At the end of the episode, when Homer leaves Moe's bar to go on a bike ride with Marge, Moe proclaims "You'll be back. And so will all of you, and you... and ''you''," whilst looking and pointing directly at the viewer, [[FourthWallPsych before quickly cutting to a different shot to show he was talking to Barney]].
* MadeOfIron: In order to prevent him from driving drunk, Homer punches Barney in the face, clubs him with a crowbar, and slams the car door on his head five times to no effect.
* StatusQuoIsGod: Anyone who is vaguely familiar with the Simpsons knows that Homer's sobriety is short lived (he's back the drinking the next episode). It dampens the heartwarming ending on rewatch.
* YoungerThanHeLooks: Hans Moleman is revealed to be 31 years old and looks old because of severe alcoholism. Before anyone cries "NegativeContinuity!", this does tie in with the birth date on his driver's license, as seen in "Selma's Choice," which is August 2, 1961 (which would make him around 31 to 32 years old at the time of this episode's premiere).