The villains of A Brother's Price. They seem to consider hammering on others' Berserk Buttons to be a hobby, based on such idiocies as not only setting off the princesses by kidnapping their new husband, but also setting off his birth family, who are very loyal to their sisters-in-law and very skilled in combat. Of course, lack of brainpower does seem to run in the family, since their brother, the previous Prince Consort, got himself killed by failing to get clear of a bomb that he knew was going to go off and when in time.
Many examples in the works of Charles Birkin. A prominent example is his short story "Ballet Negre". A London theatre critic goes to see a Haitian ballet company perform a story about zombies; finishing with a pas de deux between two convincingly zombie-like performers dancing over actual flames. The journalist becomes obsessed with trying to get an interview with them. He finds out that the two don't travel with the rest of the company and no one is allowed to see them (with different people giving conflicting explanations as to why.) Then he breaks into their hotel where he discovers that the two dancers lie on a bed all day, can barely speak except to repeat the word "hungry", look grey and corpse-like, and don't have pulses. Naturally, he comes to the conclusion that ... they are drug addicts, and he's going to expose the ballet company for drugging its stars! He breaks into the hotel again, and gives the two corned beef sandwiches to eat. To the surprise of absolutely no one reading, they are real zombies, and now they've tasted meat they want more. It's not pretty.
In Belgarath The Sorcerer the titular character recounted his time learning how to summon demons. One of his instructors, a highly-skilled magician, tried to grand-stand in his instruction by drawing a protective sigil in flame on top of a river before summoning a demon lord. He failed to take into account the fact that the sigil was washed downstream while he stood still, and was promptly eaten.
Samson from The Bible was imbued with superhuman strength by God, on the condition that he never cut his hair. He is tasked with saving the Israelites from the invading Philistines, which he does on a few occasions. Then one day he meets a Philistine woman named Delilah and falls in love with her. Delilah is in league with Samson's enemies however, and she repeatedly badgers Samson to tell her the secret to his strength and how to neutralize him. Each time Samson gives her a fake answer, and each time Delilah performs the actions which would supposedly deprive Samson of his strength (while he slept). Despite her showing her true colors multiple times, Samson doesn't wise up to this and eventually tells her that cutting his hair would eliminate his strength. So Delilah does her thing, Samson wakes up to find himself emasculated, and the Philistines come to cart him off to captivity.
Said enemies, the Philistines, deserve a mention as well for allowing Samson to grow his hair back, even though they know it's what his superhuman strength springs from.
Jacky in the last book of Bloody Jack is on the run from the US government. Not only does she not try to get out of the country, but she keeps corresponding with her known associates, and telling them where she is.
Peter in The Boy Who Reversed Himself. He is sacrificed to a man-eating boar (he lives anyway) because Laura and Omar don't consider him worth saving. Besides, it was Peter that got them stuck in the 4th Dimension in the first place due to his stupidity.
The four brats in Charlie and the Chocolate Factory all foolishly endanger their lives by going after something they want in the Wonka Factory without heeding Mr. Wonka's warnings: Augustus can't swim but decides to drink directly from a chocolate river (he falls in and is sucked up a pipe), Violet chews a piece of experimental gum (and turns into a blueberry), Veruca tries stealing a trained squirrel (the rodents toss her down a garbage chute), and Mike decides to test a teleporter on himself (and winds up shrunk). While none of them die, only Veruca isn't permanently physically altered in the process of being saved. In the 2013 stage musical adaptation, the first three kids actually perish for their foolishness, though Augustus and Violet might be saved or given a Disney Death offstage.
Burt, the lead character of the Stephen King short story "Children of the Corn" is a particularly terrible example of Too Dumb to Live. He takes far too long to admit to himself that something is seriously wrong in the town of Gatlin... and even once he does, decides to linger just to make his wife — who realized much earlier and wanted to leave immediately — squirm. This results in both of them dying horrible and otherwise completely avoidable deaths.
In the Choose Your Own Adventure book "Daredevil Park", you can choose to stay instead of going out to explore, well, Daredevil Park. In this case, your character will hang around a bit, play a few video games, take notice of the big fancy bathtub, then decide to take a bath while playing video games. It's hardly a surprise that this almost immediately leads to death by electrocution.
Feet of Clay features a Running Gag about a vampire whose employment choices (including holy water bottler, sunglasses tester, picket fence builder and worker in a pencil factory) take it Up to Eleven, seeming to indicate an intense desire to end his afterlife.
By the usual Genre SavvyDiscworld population, any examples of Too Dumb to Live that result in the person getting killed are marked down as "suicide" by the City Watch. There are a lot of ways to commit suicide in Ankh-Morpork. Walking into the Drum calling yourself "Vincent the Invulnerable" is just the icing on the cake.
Calling a dwarf short stuff or lawn gnome is also suicide, considering the insulted dwarf most likely possesses a very sharp pickaxe about his person.
Wandering into the Shades in Ankh Morpork is also a definite form of suicide.
A great moment in Feet of Clay:
''The screams stopped, and Angua walked back in, adjusting her armour. Vimes raised an eyebrow.
"Only flesh wounds." She assured him.
"Hm, okay, I think you'd better put down their wounds as self-inflicted in your report." He replied.
"Self inflicted, sir?" Carrot asked.
"Captain, they took Angua hostage."
"Ah yes. Yes, self-inflicted."''
On Twoflower: "Let's just say that if complete and utter chaos was lightning, he'd be the sort to stand on a hilltop in a thunderstorm wearing wet copper armour and shouting 'All gods are bastards'."
The all-volunteer Lancre Mountain Rescue Team have an even less tolerant attitude to Too Dumb to Live than the Ankh-Morpork Watch. They're happy to help people who are in trouble through no fault of their own, but if they have to risk their lives for someone who thought it'd be fun to go mountaineering in slippers, with a length of clothesline for the difficult bits, they may take him further up the mountain and leave him there. Stupidity kills, so it's best if it kills the stupid before they take someone else with them.
The Legends of Dune prequels: the machine empire is many times bigger than the League of Nobles, with hundreds of planets, and robots working around the clock on every one of them. They could easily create enough nuclear missiles to take out the dozen or so Noble planets in one swift strike. They don't. We learn that they can't reach the planets because they are surrounded by an atmospheric shield that fries robot brains; but why not simply firing nukes from above the atmosphere, straight down? Especially since every planet in the Duneverse is a Planetville.
In the Dale Brown novel Edge of Battle, Zakharov criticises the prison-breaking illegal immigrants as this, saying that if they had ran for the border rather than trying to take on a Mini-Mecha they would still be alive.
In the "Eternal Champion" story by Michael Moorcock, at the climax, we have a very large (million people) Middle-Age level technology army, equipped with the typical armor, horses, spears and swords. Their leader has JUST seen a demonstration of a highly-advanced ray gun which shot a HUGE bolt of fire into the air. Said weapon caused the generals' faces to turn white at the display of VASTLY superior firepower. The owners of the advanced weapon BEG the leader to leave in peace and PROMISE no harm will come to them. The leader's incredibly dumb decision is to fight. The million man army (and said leader) is literally torched to ashes within minutes.
The Yemeni in Executive Intent. After the Chinese prove they're not going to be soft-hearted like the West with their Disproportionate Retribution takeover of Mogadishu, the Yemeni still bomb a Chinese frigate. No prizes for guessing whose shit is going to get wrecked.
In a case where Too Dumb to Live is apparently contagious, Robert Bloch's Cthulhu Mythos story "Fane of the Black Pharaoh" concerns an archeologist who's lured to a hidden Egyptian tomb that has prophetic depictions of the future on its walls. He walks past centuries of illustrated history, never suspecting his death-cultist guide is going to murder him, despite seeing one picture after another in which previous foreign visitors have been led there by death-cult members and killed. Not only does he stride obliviously to his own death, blind to the implications of his predecessors' fates, but apparently is only the latest idiot to do so, among centuries of similar idiots!
Victor Frankenstein of Mary Shelley's original novel, decides to run away from, and afterwards basically forget about, his completely successfulexperiment in the creation of new life, after he decides that the result is uglier looking than he expected. He is then surprised when said creation feels epically neglected and decides to kill him.
Not only that, but all the monster wants is familial love at first and then a female companion. Victor starts making one to appease it, then gets afraid the two of them would spawn a race of monsters, so he destroys the unfinished female, which prompts the monster to commit new murders in revenge. Victor never considers that he could just leave out some of the plumbing. Not only that, but despite knowing the monster has a history of killing the people that he, Victor, loves, despite knowing that it considers him guilty for the death of its 'bride', despite its explicit warning that it will "be with you on your wedding night," when Victor marries Elizabeth he assumes that he is the monster's next target, and sends his new wife away to wait in her room completely unprotected. The results are predictable.
Averted in Gaudy Night by Dorothy L Sayers. The heroine gets a call ostensibly from the Warden's maid saying there had been an incident. She remembers all the silly heroines in adventure novels who get in trouble by not verifying and call's the Warden's quarters back.
In the Gaunt's Ghosts novel His Last Command, Gaunt has a group of enemies under his guns when one of them reaches for a gun. Gaunt calls him an idiot and shoots him.
In The Girls of Death by Helen Grant, the main protagonist is a 10 year old girl. When young girls at her school start being murdered, she starts an investigation to find the murderer, which among others includes long night activities and run ins with the underworld. As a result, not only does she drastically increase her chances of becoming the murderer's next victim, but she is also subject to other random dangers from the shady persons she interacts with.
Dolores Umbridge. Surrounded by centaurs aiming arrows at you... and you still insult them for being "filthy half-breeds"? Dumbledore has to personally bail her out of that one - and she's not even grateful for it in the slightest!
And Voldemort, who keeps using the same Killing Spell on the one kid it clearly doesn't work on, until it finally fails so epically it kills him. (To be fair: He's only got about one-eighth of his soul left in his body, which is literally held together by magic, and is sociopathically cruel and arrogant.)
Lucius Malfoy in the second film, who tries to cast the above mentioned killing spell on Harry right outside of Dumbledore's office.
Mr. Weasley: Harry, promise me that whatever you do, you will not go looking for him.
Harry: Mr. Weasley, why would I go looking for someone who wanted to kill me?
Then played hilariously straight, as he feels an urge to go looking for Black after he finds out some of the Awful Truth. He ends up hating Sirius so much that, when they meet at the end of the book, Harry charges at him and tries to choke him with his bare hands, forgetting that he was unarmed, much weaker than Black, and that Black had several wands on him at the time. Lucky for him, Black was there to protect Harry, not kill him.
In all fairness, Harry's got so many people after him that if he wants to go looking for someone who wanted to kill him, he doesn't have to go very far.
In general though, Harry's reckless curiosity does bring him into trouble and Dumbledore, enables this reckless curiosity.
Vincent Crabbe casting Fiendfyre, a jinx so deadly and unpredictable that even Hermione was afraid to try it. For most of the series, he and Goyle were portrayed as too stupid to think without Malfoy. In the second book, they choose to eat cakes left in a random location without showing the slightest suspicion. The film makes it even more jarring when they eat the cakes which are floating in midair.
Vernon Dursley. When Hagrid shows up Vernon spends the complete time acting like an abusive jerk to Harry and insulting his parents and Dumbledore, that after knowing Hagrid really cares for them. Have I mentioned Hagrid is a half giant with Super Strength and he can use magic? Althought is Dudley ends paying for it instead his father.
Dudley proves that stupidity is in the Dursley genome, particularly in the fifth book, when he taunts Harry over his PTSD regarding what happened in the previous book. Even more so in the film, where he also brings Harry's deceased mother into it. Even though using magic outside of school is still illegal for Harry, he still comes dangerously close to doing something unpleasant to Dudley.
Dumbledore is ultimately done in by a moment of stupidity. When he found one of Voldemort's Horcruxes and realized it was the Resurrection Stone, he hastily put it on his finger so he could see his family again and beg their forgiveness for failing them. Dumbledore forgot that it was still Voldemort's Horcrux, one that he knew Voldemort probably cursed. Dumbeldore falls victim to the curse, and despite Snape containing the curse in Dumbledore's now withered hand, Dumbledore still had less than a year to live. Dumbledore even admits to Harry that he was an idiot.
In Hell's Gate, we have (Commander of) Fifty (possibly roughly equivalent to a lieutenant) Shevan Garlath, whose stupidity promptly leads to the first Arcanan/Sharonan bloodbath. He died in said bloodbath, fittingly enough.
Of course, the implication was that Gandalf successfully got them so busy arguing that they simply lost track of the time and didn't notice it was getting to dawn. Of course, one would assume that with such a weakness, the trolls would have the sense to take better care, but yeah...
Word of God says that most trolls are extremely low in intelligence and the mere fact that these three could speak basic English meant they were the troll equivalents of astrophysicists.
Pavel Young from the series is a villainous example. His pinnacle of stupidity may have to be raping his own chief of security, which unsurprisingly happens shortly before his death. Raping his own chief of security by force would be bad enough — and in character, too. But no, Pavel's not quite that smart. No. He rapes her by blackmail and then has her set up the murder of Honor's lover. So, when she quietly makes sure the information on where to find the killer can be found, who can in turn tell Honor who hired him, it really comes as no surprise to those of us who aren't Too Dumb to Live.
In addition, when planning to rape Harrington herself, he failed to put two and two together in that:
He realised that she used the gym alone in the dead of night, and
She was on the Saganami Island unarmed combat team. Add to that that she's from a heavy-gravity planet and her family had been genetically modified to cope with that, he was lucky to get away with just broken bones.
Pretty much any flag officer in the Solarian League Navy. Seriously. The only one shown yet who's even remotely competent is planning to defect from the League as soon as possible. The rest are self-serving, belligerent assholes who all ignore the many reports of their enemy's vastly superior technology. And then get blown to chunky salsa for their pains.
Not to mention that Honor herself has demonstrated a pattern of sneaky tactics, misdirection, concealing her intentions and disguising her forces. Her enemies, who have often studied her tactics in detail, then routinely see exactly what she wants them to see, decide "Oh, she's just screwed up this time", and charge straight into her traps. The one time they didn't? Was the one time she was actually running a bluff.
As Katniss said in The Hunger Games, when the girl lights a campfire, at night, which makes her a sitting duck for the Careers who viciously attack and kill her, "Stupid people are dangerous."
Vee fits this trope as she goes to break into the school with Jules and Elliot, despite the fact that Elliot physically threatened Nora earlier in the novel. She also finds out that a mysterious stalker is frightening Nora so her brilliant plan is not to talk to an employee at the store they're in for help, but to disguise herself as Nora, lead the stalker off into a graveyard, have Nora follow after, and between them confront a potentially armed and dangerous person. This, unsurprisingly, leads to Vee being concussed and having her arm broken. And immediately after she gets out of the hospital, she decides that they ought to go poking around and spy on the guy who they think attacked her to begin with.
Nora also proves herself to fit this trope. A prime example would be when she is stranded in Portland and accepts a ride home from Patch, even though he chased her through a parking lot and scared her not so long ago. She then just stands there while he arranges for them to spend the night in a motel together, and apparently thinks she can hold off Patch (who has repeatedly proven to be stronger than her) if he tries anything. She later is point-blank told by Patch that he has planned to murder her and knows that he can influence her thoughts and feelings and still thinks it's a good idea to date him!!!
In Death: Some of the murder victims completely qualify for this trope. Tiara Kent from Eternity In Death stands out the most, because she had a boyfriend who had her convinced that he was a vampire and he could make her into one. She shut off the security system like he asked her to, and never considered that he needed to keep his face from being seen on the cameras. She drank a concoction like he asked her to, and never considered that it might contain rape drugs and other lovely ingredients in it. She has sex with him, and he drains her blood, resulting in her death. She didn't change into a vampire, by the way. Eve and Peabody even discuss the victim's stupidity, and Peabody explains that the victim was a rich, spoiled girl who was not known for her brains.
Governor Aubert of David Weber's In Fury Born is a subversion. When we first meet him, he's ignoring the warnings of the elite Marines stationed on Gyangtse, instead listening to the advice of his even stupider advisor, Salgado, which results in a major uprising by separatist forces. However, when said uprising occurs, Aubert realizes his stupidity, fires his advisor, and aids the Marines in resolving the conflict.
In Inheritance of the Inheritance Cycle, King Orrin takes this Up to Eleven with his plan to send an envoy to Galbatorix, try to negotiate a peace agreement, and tell him the Varden's position. Because to do otherwise would be discourteous.
At the end of Brisingr, Eragon and Arya abandon his elven guard and go see the queen themselves. Naturally, they end up badly outmatched.
Iron Druid Chronicles. Atticus fakes his death and the Morrigan, the Celtic Chooser of the Slain shows up to "claim his soul" and reclaim a Magic Sword he had stolen from the Tuatha De Dannan back in the day. One of his would-be killers, the Norse god Vidar, tries to claim the sword as the spoils of victory but the Morrigan says oh heck no. When he tries to get uppity with her she offers to let him win it off her in a sword fight. Just to reiterate. The Morrigan is a psychopomp. Not just any old psychopomp, but a chooser of the slain. Meaning she can choose who dies in battle. What's more, that magic sword they're fighting over? Its ability is to go "not happening" at any armor that gets in its way. It goes about as well as you might expect.
In Ken Follett's World War II thriller Jackdaws, Flick Clairet leads her Strategic Operations Executive commandoteam behind enemy lines in occupied France. While in Paris, Flick arranges for the team to stay at an out-of-the way flophouse who proprietor Flick knows to be sympathetic to the resistance. But one team member, Maude, wants to stay at the Ritz, the famous Parisian luxury hotel, and had previously convinced another team member, her girlfriend Diana, to take her there. When Flick hears this, she is appalled at Maude's stupidity, asking her "What world do you live in?" Sure enough, pretty much as soon as Flick's back is turned, Diana and Maude sneak out of the flophouse to go check into the Ritz, never mind that it is pretty much the Gestapo headquarters in Paris. Needless to say, they get arrested in the main dining room in a matter of minutes.
Tang Sanzang of Journey to the West definitely qualifies. Despite having three demonic bodyguards constantly warning him about the evil nature of the strangers that they encounter he constantly disregards their advice because he can't see the forest through the trees. Even after being captured and nearly cooked alive multiple times Sanzang still doesn't understand that beauty doesn't equal good.
Judge and Jury, by James Patterson and Andrew Gross, is about the trial of a mob leader who is a powerful sociopath. The judge lets him hear the jury's names during selection. Even after he gets someone to break into her alarmed house, leave the evening paper under her pillow, and all but openly threatens her, she does nothing. By the end of the day, all but one of the jurors is dead to a bomb. The retrial is locked down like Fort Knox.
Michael from the Knight and Rogue Series makes a habit of seeking out killers, and will knowingly walk into traps that are pretty much always set to get him, a man with no legal rights, framed for a hanging crime. Even if this is to save lives or try and at least see who's setting you up, when you're the sort of protagonist who usually gets at least two good beating a book and have people wanting you executed just for getting into a street fight, this is a very bad idea.
The Kzinti from Larry Niven's Known Space series. While they are formidable-looking 8' tall, 500-pound tiger-men, a combination of room-temperature IQ and uncontrollable hair-trigger tempers means that they ALWAYS lose, even in hand to hand combat with humans 1/3 their mass. Specifically, their only tactic is "scream and leap". Niven, actual cats know more complicated tactics than that. Part of it can be chalked up to Honor Before Reason, but societies whose honor codes start hurting them learn how to Rules Lawyer the honor code pretty fast, if they don't junk it outright. Even worse, their race supposedly got its space-age tech by overthrowing an advanced spacefaring civilization that conquered their planet. How the heck they managed to do so despite their above-described dumbassery is anyone's guess.
They did so before they were that dumb. They were tribal warrior primitives before they overthrew the spacefarers and stole their tech. Then they used the biotech they'd stolen to genetically engineer themselves to be perfect - as defined by a primitive tribal warrior culture, i.e. massively aggressive, status-conscious, and utterly truthful. They actually rebuilt their descendants to be unable to Rules Lawyer their honor code. This doesn't change much until evolution kicks back in... once they attack humans.
The Pak protectors deserve special mention, as it's their very intellectual brilliance (which is not the same as wisdom) that condemns them to eternal war. They're so good at calculating the odds of gaining an advantage for their own offspring, and so hidebound by their compulsion to seize such opportunities instantly, that they're unable to consider alternatives that might be marginally more risky, yet could provide a greater, more lasting benefit (e.g. interbreeding their offspring with other protectors' so they become eternal allies rather than destroying one another on sight).
Carpathia's plan in Left Behind is to follow every step of the divine plan that leads to his inevitable defeat, as opposing to try and Screw Destiny by, for example, ruling fairly and trying to create a better world, or just nuking the whole planet to spite Him. Well okay, he did intend to deviate from the plan at the last possible minute by waiting until Jesus actually returned and then shooting him. This works about as well as you'd expect.
Not like Carpathia totally had a choice, if he was to fulfill every aspect of The Bible prophecies concerning the Antichrist. But like Satan, Nicolae thinks he's got a chance of ascending to the heights of the clouds and becoming like the Most High, so it's not just being Too Dumb to Live, but also too arrogant.
The people who live through the Tribulation who refuse to believe in God and Jesus Christ, despite growing evidence that it is His hand at work pouring out the judgments, also qualify.
"... some girl who can't tell the difference between a wolf and her grandmother must either have been as dense as teak or come from an extremely ugly family."
The modern version rubs salt in the wound by producing an awful mixture of Deus ex Machina, Unexplained Recovery, and Bowdlerisation. Not only does she suffer nothing for her impressive stupidity, but the original version's moral of "don't trust strangers" is completely dropped in favor of a happy ending.
In The Long Walk, a walker who dies early on was wearing sneakers, despite the rulebook that the contestants were given in advance explicitly telling them not to do so, as no other type of footwear will help develop blisters faster on long distances. Predictably, he develops blisters pretty soon, and is ticketed after walking at the required speed becomes too painful for him one time too many. Garraty even discusses it in his internal monologue.
Pippin in The Lord of the Rings. Even if you don't count the first time ("Ooh, we're in a dark scary place that Gandalf wants us to move through quickly, but there's a big hole in the ground and I wanna see how deep it is... let's drop a stone!"), there's still this lovely number. "I have to look at it! I'll take it from the wizard when he's sleeping! But, hey! This time he doesn't have a perfectly good reason for not letting me see the shiny rock that Saruman used to communicate with Sauron! Even though he's older than the world and I already killed him once."
It's pretty explicit that the palantiri are addictive for people who aren't very strong-willed, at least if the person they've got on speed-dial is Sauron.
The early versions of The Return of the King had Pippin getting killed. The only thing that saved him was Tolkien wanted him to live. Too Dumb indeed.
In the third Mercy Thompson novel, several kids beat up Jesse Hauptmann precisely because her father is a werewolf. If Jesse hadn't refused to tell her father their names, he would have killed them.
Moon Crash Series: Even though she has been living in an area with no reliable electricity, and brownouts that last for days, Bri decides to take an elevator in her apartment building, and dies when she is trapped in there for days.
A tangential example in Heinlein's "The Moon Is a Harsh Mistress." When the rebelling lunar colony starts throwing 100 ton rocks from orbit, they explicitly target highly visible but mostly unoccupied places, since this is an intimidation tactic: they want the Earthlings to know that they could flatten cities if they wanted to, but not to have to actually kill millions. Even so, in the first round of strikes, thousands of people (mostly in North America) decide that this is so little of a threat they pack picnics and go to the target sites to watch... even though these impacts had the power of a small nuclear bomb. The rubberneckers got predictably dead.
And after this happens, a random Congressman decides to personally blame Mannie (the protagonist/narrator) for it in a highly insulting and sanctimonious fashion. While Mannie, as Luna's military commander, was responsible for the bombing, he was not (as he points out) responsible for the actions of anyone stupid enough to ignore his repeated warnings. Note that Mannie was on the tail end of a very long and stressful day, had been up for over 24 hours at this point, and has zero tolerance for fools even under the best circumstances. Add to this the fact that impropriety is considered an elimination-worthy offense in Luna. Mannie eventually delivers a "him or me" ultimatum and storms out before he does something he'll regret. He mentions a little later that he never saw that Congressman again after that.
Simon in The Mortal Instruments. Breaking into a hotel of murderous vampires that have expressed that they wouldn't mind having an excuse to turn you into hamburger meat isn't such a good idea. Especially if you go alone. And do it at night. Sure the vampire blood was summoning him back to Raphael, and he would have given in and sought them out sooner or later, but if he had only asked Luke, he would have known to wait a few more days, and the blood would have gone out of his system, as well as the compulsion it had on him to return to Raphael.
Some young cats in the Warrior CatsCode Of The Clans story, "A Night Of Listening", plan on jumping into the gorge after injuring themselves in games. If it weren't for medicine cat Meadowpelt finding an answer from StarClan, they would be dead already.
In No Country for Old Men, Llewelyn Moss literally gives this trope to the dead gangster he tries to bring water to when he comes back by night to the scene of the shooting. Apparently the said gangster (though he was indeed wounded) just sat there waiting for the man who ultimately came and finished him off, and therefore...
Llewelyn: Here you are. Too dumb to live.
In Oath of Fealty by Larry Niven and Jerry Pournelle, the plot is initiated by a group of teenagers who, as a prank, try to sneak into a heavily surveillance filled arcology while carrying a box labeled "bomb". They take just enough precautions to defeat all of the nonlethal methods of stopping them. The abject stupidity of this act is very heavily lampshaded, and spawns the repeated phrase "Think of it as evolution in action." At one point they even break through a door which has a sign that warns, "If you enter here YOU WILL DIE!" Among other skull and crossbones-type warnings.
The father in the 1998 Newbery Medal winner Out Of The Dust instigates the main plot of the book by leaving a pail of kerosene by the stove. A pile of highly combustible fuel that has a flashpoint of roughly 100-150 degrees Fahrenheit and that gives off toxic fumes. Not to mention that, since it's oil, it's hard to extinguish with water...
A particularly egregious example is when they enter Hephaestus' junkyard and after explicitly being told not to touch or take anything, everyone does exactly that. Bianca's death was likely only because she drew the short straw offscreen.
It's even worse for Grover. When told not to touch anything in the junkyard, his immediate response is to pick up a golden crown and bite a piece off! Guess his unconscious eating habits got the better of him.
It is a well known fact that demigods dreams can show the future, or even something important about the present. Percy is particularly fond of having prophetic dreams, but he never tells them to anybody!
Percy Jackson in general. When Annabeth leaves him to think on his own in the third book, he's pretty much helpless. His solution for an indestructible lion is to throw food at it. His solution for possessing both an indestructible jacket and a creature that could potentially topple the gods is to toss them both into the ocean and hope for the best. The only reason Dionysus lets him go on a quest without Annabeth to think for him is because he thinks he'll die. Unfortunately, he ends up killing Zoe and Bianca with his stupidity instead.
This continues in this Percy Jackson followup series where the heroes tend to make the same mistakes. What is worse is the gods. Zeus knows the giants cannot be defeated without the aid of the demigods so what does he choose to do? Seal up Olympus and ignore the problem repeating the same mistake he made with the Titans. Throughout all of the books, Zeus makes a series of "too dumb to live" mistakes. Ladies and Gentlemen, the ruler of the world!
Alcyoneus, as pointed out by Frank - when you're unkillable as long as you stay in the boundaries of the state of Alaska, you really shouldn't hang out in the part of the state that's only 10 miles wide.
Frank: "Welcome to Canada, idiot."
Dion from the Conan the Barbarian story, "The Phoenix on the Sword." When the chief slave of the guy who plans to have Conan killed tells you that he was once a powerful sorcerer of Stygia, and is clearly obsessed with getting back a lost Ring of Power that was stolen from him by a Shemitish thief — and you have a "ring of good fortune" that just so happens to have been stolen from a sorcerer of Stygia by a Shemitish thief — it just might not be a good idea to bring up this little fact around the guy, much less actually show him the ring. Dion's swinish stupidity promptly gets him stabinated as Thoth-Amon reclaims his ring and sets out to unleash the unholiest vengeance upon his former master.
Jacob Esterbrook, in Rage of a Demon King, is urged repeatedly to evacuate from the path of an oncoming army, one so huge that the plans for fighting it are "make a scorched-earth retreat to defensible lines, then starve the army over the winter". He's convinced that his skills as a merchant and diplomat will let him make a negotiated settlement between his employer and the leaders of the army. The first soldiers to encounter him are a pair of scouts from a cannibal tribe...
In the Rainbow Magic series, Rachel and Kirsty have had to save the goblins from being hurt by their own stupidity many times.
In The Relic, there's a mysterious creature killing people in the New York City Museum of Natural History and eating their brains. It's a known fact that these killings happen after nightfall and they always occur in the exhibit hall, so it's warned that all the museum workers should clear out of the exhibit hall before nightfall until these killings are solved. Late in the book one of the workers heads into the exhibit hall after midnight to relieve some stress by engaging in his personal hobby at look at some of the rare artifacts, in spite of the fact that he's been warned that doing so is dangerous ground. True to form, he winds up becoming another victim.
In Alastair ReynoldsRevelation Space novels, whichever moron invented the Greenfly - self replicating robots whose only directive is: Modify all matter in the Universe into the form most efficient for the growth of plants. The latter books and stories show they succeed in this to the extent possible in the lifetime of the universe. Given that FTL flight is not possible in this universe, there's no conceivable use for the Greenfly on a solar system wide level (there are too few near-FTL ships to make importing food economic). It is conceivable that they would be of use in inhabited systems where they could convert spare asteroids etc. So why build them to have such blind ambition? Hell, why give them the ability to think at all given the problems humanity had with the Inhibitors?
Romance of the Three Kingdoms. Ma Su. Good God, Ma Su. During the Shu Kingdom's expedition against the Wei Kingdom, Ma Su was put in charge of defending Jie Ting, a very important location for the Shu forces. The location is near a mountain so Ma Su thought it would be a good idea to camp at the top of the mountain. Normally this would be a good idea, EXCEPT in this case, if they camped at the mountain and Wei surrounds them, their water supply at the bottom of the mountain would be cut off. Pretty much everybody except Ma Su sees this and he even ignores their warnings and proceeds to camp at the mountain. Guess what happened.
In 'Salem's Lot by Stephen King, Susan Norton, despite being warned by Ben Mears and Matt Burke that they should stay away from the Marsten House for now, goes there all on her own to see if there's really a vampire there. What's more, on the way she encounters twelve year old Mark Petrie who actually has warded off a vampire the previous night. Now, with proof and a new ally, does she suggest that the two of them go back to town and get reinforcements to return in force? No, she and Mark go up to the house all on their own. What do you think happens?
Most of the adults in Lemony Snicket's A Series of Unfortunate Events. Their apparent blindness to Count Olaf's Schemes result in several murders, mobs, and razed buildings.
Siege Of Darkness. The drow forces are split into two groups: one attacking Mithral Hall from underground, and the other attacking from the surface. During the planning stages, everybody seemingly forgot that drow eyes cannot tolerate sunlight unless they've become used to it. Or perhaps none of them thought that the battle would last the entire night and that they would still be fighting the good guys when the sun came up. In any case, when the dawn comes, the drow on the surface are blinded and pretty well screwed.
The drow expected the sun to come up and even trained looking at light to be prepared for it. They just greatly overestimated their tolerance for sunlight, as it was the first time they actually saw it.
Viserys. Threatening the wife of a barbarian chieftain in front of said chieftain, with your sword out in the barbarian's holy city where it's forbidden? And where you're surrounded by some twenty thousand of said chieftain's people? What could possibly go wrong?
Ned. Ned, Ned, Ned, Ned, Ned. So here's the guy who has a crush on your wife and tells you explicitly not to trust him? Well, trust him! So the queen is fucking her twin brother, has three incest children and might have had a part in killing the king? Tell her that you know enough to get her killed! Oh, and said king? He is on his deathbed— this is the time to be tactful and not to tell him what you know, even though it could have saved the country from a civil war. And when the King's brother suggests a plan to avert years of war and the deaths of millions? Blow him off! Great job!
Like father, like son. Congratulations on marrying the first girl you slept with, Robb, even though you have just broken your arranged marriage pact. Even worse, relying on Roose Bolton to lead a significant part of your forces while out of your sight even though his house has been opposed to yours for its entire existence and he has a tendency to get your allies to suffer oddly high casualties.
Tell you what, unstable queen who's been belittled and insulted for hours, they'll sell you their entire army of fanatically loyal super soldiers who will obey any command for one of your fanatically loyal baby dragons. An army is nothing compared to a baby dragon, after all! You may call this idiocy, but in Astapor, they call it good business!
Also, belittling the son you despised since he was born while said son — who is, by the way, convicted on charges on regicide and kinslaying and sentenced to die — is holding a crossbow at you is a great idea. Right, Tywin?
Some people might spot the slight flaw in any plan which involves enraging almost everybody with an army on the continent thanks to breaking social conventions so basic, they aren't even written down as distinct laws. And, the only thing that is kind of holding back the slaughter is having their relatives as hostages... who you will have to think about giving back probably sooner rather than later. But, not the Freys. How is that working out, guys?
Flouting direct orders is a great way to keep your head. Especially if your Commander just spent the last several months among savage raiders. And you locked him in the cooler, literally, for a few days. And tried to get him killed. And had a hand in killing his father. Surely Lord Snow only meant to give you a haircut, right Janos?
"I took Dragon Taming 101, how hard can it be to tame two dragons?" Well, how hard is it, Quentyn?
A special mention for a couple of minor characters thanks to the sheer dumbness. Well done, SerBalmanByrch: trying to kill Bronn in a jousting session was a really incredibly well thought-out plan that couldn't possibly backfire. Worse, your wife, Lady Falyse Stokeworth, wouldn't want to compound the problem by running to such a reliable "employer" as Cersei Lannister expecting help after your inevitable screw-up... I mean... death, now, would she? Congratulations, you two. Ten out of ten for teamwork.
Arys Oakheart's death is so stupid that one observer wonders if he wasn't trying for Suicide by Cop.
An example from before the books but still. Lord Luthor Tyrel, the current Lord Tyrel's father and wife to Olenna Tyrell, died while hawking. He was riding a horse and was too focused on what his hawk was doing he rode off a cliff. Clearly his surviving progeny got their wits from their mother instead.
In Michael Flynn's Spiral Arm novel On the Razor's Edge, at the end Mearana is told she's too stupid to live, and usually they would accommodate her, but as things are not usual, they will send her back over the Rift.
T'Lana from the Star Trek pocket books is a very short-lived character in the current Borg Story Arc for just this reason. From the first book she is introduced in she immediately questions the judgment of practically everybody on board the ship who isn't a Vulcan, she objects to nearly every action anyone ranked above her takes, and spearheads a mutiny with other members of the senior staff against Picard, only to give command back to him refusing to simply admit that she fucked up majorly. Even Spock eventually just walks away during a conversation with her, after calling her the Vulcan equivalent of a dim-witted jerkass. At the end of the second book she appears in, Picard wants her gone, which means something when his current first officer once defected to the Klingon Empire and thus could, very technically, be called a traitor. Her ultimate fate? She's replaced with Genki Girl T'ryssa Chen, a half-vulcan who prefers her human side and roleplaying as an elf, and gets blown into powder when the Borg partially glass Vulcan.
In the Star Wars Expanded Universe novels this pretty much sums up the New Republic/Galactic Federation of Free Alliances. The Old Republic lasted "a thousand generations". The New Republic lasted less than one, largely because it was so mired in politics that it was wholly unable to adequately respond to an extragalactic invasion. Thanks to the tireless efforts of our passionately individualistic heroes the invaders are eventually stopped and the Galactic Federation of Free Alliances is formed. During its brief existence it has allowed a Sith Lord to exploit a legal technicality to seize power, the second time this had occurred in less than a century. Once our heroes sort that out, the GFFA then arbitrarily appoints a former enemy who once tried, unsuccessfully, to destroy their capital planet as their new Chief of State for no apparent reason other than that a real election would be too much trouble and there were seemingly no qualified candidates amongst the ranks of their own government. Needless to say, more trouble quickly ensues. All of this keeps the Jedi in a role of constantly having to oppose their own government and likewise routinely being out of favor with said government, who are deeply offended by the Jedi's ceaseless attempts to stop their lemming-like drive towards self-destruction.
The latest Galactic Government, the Galactic Federation Triumvirate seems destined to fail too: The Empire forms one branch, the New Republic another, and a Jedi the third.
The Fel Empire decided it was a good idea to side with the One Sith, sure they are different from the previous Sith, but they still have the same old Chronic Backstabbing Disorder prevalent among them and won't settle to being second banana to anyone.
Ivan in "Tsarevitch Ivan, the Fire Bird and the Gray Wolf." He double-subverts Youngest Child Wins in that, while in many other fairy tales the older siblings are the ones to disregard the instructions and the youngest wins by doing what they're supposed to, Ivan is the one who repeatedly touches things he's been specifically told not to while trying to steal the Firebird etc., trips magical burglar alarms, and gets sent on one Fetch Quest after another as a consequence (and he keeps getting told that he wouldn't have had to resort to burglary if he'd just asked). De-subverted because the wolf keeps bailing him out, even after he actually dies.
Many situations the main cast gets into could have been resolved if anyone bothered to remember they live in the twenty-first century with all of its wonderful human-made technology or if the vampires remembered that they are the top predators of the food chain. The seven-member Cullen family could have destroyed James' coven of three if they had bothered to fight! Call the Volturi, have them restrain Edward, and have Bella talk to him so he would stop being suicidal! So many incidents could have been avoided if anyone bothered to pick up a phone!
Bree and Diego from "The Short, Second Life of Bree Tanner" would surely count as well. They both know that they're being kept in a basement by a Riley, who (A) has been kidnapping other teenagers to make into vampires and (B) clearly doesn't care if they kill each other. Later on, they discover that the story they had been fed about how sunlight burns them up was a lie. They also learn that they were all being used as cannon fodder and Bree remembers that the night she had been turned into a vampire, she had been kidnapped and tricked into it. They also find out that Riley is discussing plans with Victoria. So of course they come to the conclusion that Riley is completely innocent and will surely help them if they tell him everything they know, so Diego decides to meet him alone, to tell Riley that he knows all of these secrets, without telling anyone except for Bree where he is going. Needless to say, Diego does not return. Bree qualifies as this trope because after all of that, she doesn't realize that Diego is dead until Riley has run off and left her and the other vampires to be killed by the Cullens.
In Virenzo en ik by Mireille Geus, Virenzo, who attends a sailing club, has a habit of tying his hand to one of the sail ropes "because it is easier to steer this way". One day the boat he is on capsizes and sinks, and drags him down with her.
All the authorities in the story Watchbird, by Robert Sheckley. First, they build a crowd of machines programmed to protect humans, and make them autonomous, self-taught and without any control circuit so they can be efficient, and the machines get out of control and start protecting anything, from cows to other machines, so economy, farming and stuff ends in chaos, and then, to protect humanity they build a crowd of machines programmed to kill the first ones... and these are also autonomous, self-taught and without any control circuit so they can be efficient.
Wolfbreed gives us Darien, a man who must have been born under a stupid sign. First off, he is a werewolf and grew up in a town made up entirely of werewolves. His parents and everybody in the town tell him not to let anyone outside the village know he is a werewolf or run around in wolf form in broad daylight because there is a Church MilitantBadass Army out there that has pledged to destroy werewolves. Guess what Darien does, and then after the predictable results, refuses to accept blame for his actions and projects his self-loathing onto humanity. So he starts killing innocent people to lure a unit of said army into his trap. That's right, he picks a fight with a group of about 40 elite soldiers specifically trained and armed to kill his kind and have plenty of experience doing so and then Darien has the gall to act surprised when they nearly kill him. Then he tries to convince a female werewolf that he lusts after, who has been raised by ordinary humans, that Humans Are the Real Monsters— by framing her for murder! And he does so in such a way that the girl, the soldiers and just about every other major character knows he is really responsible in about two minutes after the killing takes place!
Agatha Christie stories. You can pretty much guarantee that one of the victims saw who did it and decided it would be a smart move to blackmail the serial killer and sneak off to meet them in a lonely spot to collect the first payment.
Played with in Hallowe'en Party, where the young teen loudly shouts around about how she once saw a murder happen and ends up killed shortly after, when everyone first laughed her story off since she often told lies. Turns out the girl never saw a murder. Her friend did and told her, so she decided to make herself interesting by simply "taking over" the story.
This is a long standing complaint of fans of Romance fiction who use the abbreviation TSTL (Too Stupid to Live) to describe any heroine (or hero) who drives the plot by sending all reason and common sense on sabbatical while pursuing the love of their lives.