* To be the greatest detective of them all and save the world, you need to base all of your assumptions off of the findings of dead people. Hey, they're dead, nobody will know that evidence isn't yours--you can be a hero!
* [[BunnyEarsLawyer To be the best in your field you should ignore personal hygiene and show up to work in the clothes you slept in.]]
* ''LightNovel/AnotherNote'': Hide out in your safe house and have the FairCop you've recruited do all the work and then claim credit for solving the case when it's through. If you are the law no one can question you.
* Another one for ''LightNovel/AnotherNote'' [[TheFarmerAndTheViper If you rescue the poor little orphan]] [[AllOfTheOtherReindeer who doesn't fit in]], give him a home, steady meals, a stable environment, and the very best in education he will become your obsessed stalker [[spoiler: who commits multiple homicides [[AttentionWhore just to get your attention.]]]]
* Being an autistic orphan guarantees that you're a genius.
* And if you`re not a genius, you`re useless, even if you are very good at your job and have lots of experience.
* Self preservation is for pussies. A real detective announces his presence and harasses their mass-murder-suspect-with-an-unknown-weapon constantly.
* Don't try to [[UtopiaJustifiesTheMeans drastically change the world for the better]] unless you are prepared to turn into a [[TheSociopath sociopathic,]] [[AGodAmI delusional,]] [[MemeticMutation potato chip-munching]] maniac.
* Also, GIRLZ IZ STOOPID.
** Extension: Women are weak, incompetent and need a man to lead them (and even then they are prone to making mistakes). Once they find him, they should StayInTheKitchen.
* If you've fallen in love with someone, naturally the appropriate response is to stalk that person, have your crazy friend threaten to kill him, and dress like a whore. Your victim (I'm sorry, ''BOYFRIEND'') will grow to love you eventually.
** To be fair, [[ITakeOffenseToThatLastOne she dressed like that since well before]].
* ALL PROBLEMS ARE SOLVED WITH HANDCUFFS. If it isn't working, the handcuffs aren't small enough.
* Never mind if your ideals are completely correct--if you develop [[AGodAmI a God complex]], you must die and your work must be undone. You just wanted to make the world a better place and had to make some insignificant-in-the-grand-scheme-of-things sacrifices? Sorry, you're not a nice person, so you lose.
* [[BrokenAesop Killing criminals is only wrong if]] ''[[VigilanteMan Kira]]'' [[CantGetAwayWithNuthin does it]]. [[ScrewTheRulesIMakeThem If you have a badge and official sanction it's a-okay (you can break any number of rules that you like!)]] and [[NotSoDifferent nevermind if you get justice for the families of the victims neglected by a corrupt system, we will execute you]] [[HypocriticalHumor like the criminal you are.]]
* Writing in books is dangerous and evil. It's not a pretty picture. (Dramatic and stylised, perhaps, but not pretty.) Don't do it. Ever.
* Mass-murder is AWESOME!!! There is NOTHING it cannot do. Start slaughtering people today and you too can have a [[TheDitz hot]] [[GenkiGirl girlfriend]], steady job, [[FanDumb legions of devoted followers]], and (drumroll please) . . . world peace! Even if you die! That's right, kids, [[UtopiaJustifiesTheMeans utopia]] can be yours, just make sure you start out by bumping off criminals . . . that way, you'll be justified no matter how much of a monster you become. [[Theatre/BloodyBloodyAndrewJackson Everything you say]] and do [[Theatre/BloodyBloodyAndrewJackson is right!]] Just remember these [[RuleOfThree three simple rules]]: 1) if you think they deserve to die, they deserve to die, 2) if they get in your way, they deserve to die, and 3) if the world isn't a utopia yet, that just means you haven't killed enough people! [[SchmuckBait Act now!]] Utopia is just a drawn out mass-murder session killing away!
* The only thing more epic than writing in a notebook . . . is [[MemeticMutation eating potato chips.]] Unless you repeatedly shout "delete" whilst writing in said notebook, then the sheer epic-ness might just make you come to fruition.
* Matsuda is an idiot.
* Do nothing. Don't ever try to change the world for the better. Sit around in your room and play with toys all day and you are sure to win at life.
* If your little sister is ever kidnapped by violent criminals kill her immediately [[spoiler: because if you save her it will lead to your death.]]
* [[DysfunctionJunction If you are really smart then there is somethning wrong with you.]] [[BrokenAce Odds are that you're either evil]] [[BunnyEarsLawyer or crazy]] or both.
** Normal, well-adjusted genii have only bit parts or die horribly within 30 seconds of getting any screen time (here's looking at you, [[spoiler: Matt]]).
* Being a good student and taking notes is an executable offense.
* The L Diet: Eating lots of candy makes you rakishly thin and a genius to boot.
** Also apparently you can eat nothing but chocolate and still fit into [[PaintedOnPants tight leather pants]].
* [[spoiler: [[BrokenBase Light Yagami / L Lawliet]]]] [[EveryoneIsJesusInPurgatory died for your sins.]]
* Smoking kills by [[spoiler: getting you shot thirty times.]]
* [[HoYay If you ignore your shrill, annoying, possibly murderess "hot girlfriend" and you are chained to an exotic young male detective 24-7... you are gay.]]
* Bored student = future SerialKiller.
* "[[ForGreatJustice Justice]]" apparently means either "mass murder" or "stalking teenage boys." [[WithUsOrAgainstUs Pick a side-we're at war.]]
* No, the PowerOfFriendship will not protect you from Kira.
* Don't pick up trash you find randomly lying around at school.
* Never make mistakes. EVER! If you ever make even ONE mistake it will inevitably, irreparably screw up your life and/or get you killed-probably both. Unless your name is Matsuda...
* On that note, don't ever try to improve yourself. Being the [[ThisLoserIsYou token idiot]] comic relief [[TheWorldsExpertOnGettingKilled is much safer than being a mega-genius.]]
** Unless your name is Nate River.
* Friendship is deadly. If you make even ''one friend'' you will die.
* From the original ''Death Note Pilot'': If you find a strange notebook written in a language that you do not understand decently enough to know what 90% of written words mean, immediately begin to write in it, damned the consequences. [[TemptingFate After all, this cannot horribly backfire in any way]].