Adventures of the Gummi Bears: Sir Thornberry is a perfect example of this trope. He tends to ignore the most obvious dangers or behaves totally oblivious to consequences of his actions, e.g. in the series' grand finale, he ignores the fact that a screw is about to fall off the machine and he promptly tries to bring the machine into operation, which results in destroying the whole device. He has his rare moments of awesomeness, though. Whether he's a complete idiot or someone who's at least somewhat competent seems to be Depending on the Writer.
In the Adventure Time episode "The Limit", we meet the Hot Dog Knights, who are described by their own princess as being slow. When two of them (along with our heroes) are granted wishes:
Finn: Okay, so you guys should wish to get your buddies back right? Hot Dog Knight 1: I wish for a box! (a cardboard box appears) Sweeeet! Hot Dog Knight 2: I wish to blow up! ...I mean get big! *BOOM!* Finn: Wow, you guys are really stupid. Hot Dog Knight 1: What do you mean?
In the episode "All Your Fault", Lemongrab and his clone have turned all of the food that Princess Bubblegum has supplied them into living beings, then when Finn and Jake give them seeds to regrow their crops they bring those to life as well, and continue to blame PB for their suffering and send their largest creation to attack the Candy Kingdom. Had PB not erased the life-bringing formula from their brains at the end of the episode the Lemon Kingdom's population would be wiped out and the Candy Kingdom would be in rubble.
In "From Bad To Worse", the candy people are turned into zombies and eventually infect Jake. Jake then seals himself in a "sciency shower" to prevent himself from infecting Finn and Lady Rainicorn. Finn and Jake both tell Rainicorn not to let him out of the shower. Care to take a guess what she does?
In Aladdin: The Series Jasmine is this in the episode "When Chaos Comes Calling" where she orders Chaos, a god-like being shown to be more powerful than Mirage (who herself is a powerful evil elemental capable of wiping Agrabah easily off the map without the heroes saving the day) to stop causing madness around the palace during a royal guest meeting. Although Chaos looks like a harmless silly blue cat with wings, Genie had explicitly warned her not to make him mad as he had "more power in his whisker than a palace full of Genies" and could grant his own wishes. To no one's surprise, Chaos does not take being ordered around well and shrinks her to the size of an ant right under Aladdin's feet, who unknowingly endangers her life. Fortunately she is brought back to full size due to Chaos' love for unpredictability. Jasmine should really have known better than to order around a trickster deity.
While most of the cast of Aqua Teen Hunger Force qualifies for the Idiot Ball in some form, no one exemplifies Too Dumb to Live as well as Master Shake. Indeed, Shake repeatedly dies in many episodes (continuity is non-existent on the show), usually by his own stupidity. He has sliced himself in half with a katana, eaten a sandwich that he knew would send him to a hell dimension where an axe-wielding cyclops awaited to slice his head open, and has gone as far as committing suicide to ruin Meatwad's Ouija video game.
Another sterling example of Too Dumb to Live is an episode where the Mooninites (usually actually fairly competent by the show's standards) are menaced by a monster that wants to eradicate them, and instead of doing anything to stop this, use it as the basis for a pyramid scheme. At the same time as The Reveal that the monster was real, one of them gets a Karmic Death for his stupidity and Jerkassness when it squashes him, while he's trying to enroll it into the pyramid scheme. Truly epic instance of the Idiot Ball.
Cheryl Tunt from Archer. Nearly kills herself in "The Double Deuce" because Pam suggested it and only stops because dying would keep her from cashing in on the tontine. In "Crossing Over", she hooks up with Barry and asks him to strangle her.
The (stunningly naïve) Earth King from Avatar: The Last Airbender : Fresh from having his Evil Chancellor exposed as having deceived and manipulated him for years, he happily explains to the newly-arrived Kyoshi Warriors about the Day of the Black Sun invasion plan. Even if the Warriors weren't Azula and her sidekicks in disguise, The Earth King just openly blabbed about a major, secret military operation to a group of warriors he'd met literally seconds ago. And yes, this bites the good guys in the ass in a big way, later. Especially as the King clearly didn't bother telling them that the enemy knew because of him.
Darkstar has a moment in the Ben 10: Ultimate Alien episode "Couples Retreat". Saying that you want to take another girl as a trophy once you Take Over the World while within earshot of the girl who gave you your powers is not the best idea. Especially if the girl who gave you said powers is True Neutral at best.
The Vreedle Brothers personify this trope, so much so that they have actually been killed more than once. The best example comes when Octagon Vreedle launches a nuclear fusion grenade at Ultimate Kevin. When told that it will blow up the entire space station that they're standing in, he replies:
Batman & Mr. Freeze: SubZero gives us Gregory Belson, Mr. Freeze's sidekick. First off, he was a brilliant addition to the movie, in that he just about makes a perfect foil for Freeze's character. While Freeze was a ruthless, determined, and coldly efficient antagonist, Belson was...a bumbling moron. His first moment of stupidity is when he selects Barbara Gordon as an organ donor for Freeze's wife...who also happens to be the police chief's daughter, and Batgirl, to boot. Later, he calls his stockbroker to inform him he'll have enough money to pay off his debt...while Batman and Robin are listening, which leads them to the oil rig. Even then, when Barbara escapes before the operation can begin, Belson pulls a gun and accidentally shoots several fuel tanks (despite Babs warning him not to), starting a fire that destroys Freeze's lair. THEN, he abandons Freeze and makes off in a motorboat...only to drive right into the path of falling debris. His betrayal ends up forcing Freeze to team up with the heroes to save Nora, which eventually leads to her being cured. To break it down: He chose Batgirl as an organ donor, lead the heroes to her rescue, and then inadvertently thwarted the plan. His stupidity is what drove the plot! In Belson's defense, he didn't know Babs was Batgirl. Not to mention Freeze's wife needed a donor to fit so many characteristics it wasn't like there was anybody else he could pick. Even though with Wayne's help, Nora's doctors were able to find a donor who wasn't Barbara...
In Batman: The Animated Series, the Mad Hatter takes his secretary out on the town after a breakup. Somehow she fails to notice that everyone serving them has an extremely conspicuous card reading "In This Style 10/6" on their heads (the Hatter's mind-control device), and fails to pick up on Tetch's crush on her until it's too late.
The eponymous character in Chowder. Not only does he usually drive the plot along by either destroying something in stupidity or just by being incredibly stupid, but, well, apparently he's literally Too Dumb to Live without someone directing him. This is a guy who once thought the proper way to put away a spoon was to shove it in an electrical outlet after all (and judging from the marks it happened more than once).
There's something Daffy Duck doesn't know that Bugs Bunny does in the Duck Season-Rabbit Season trilogy of cartoons. All Bugs has to do is manipulate a little of Daffy's syntax and Daffy's demand to get blasted in the face with Elmer's rifle will be granted. He virtually pleads for it at the near end of "Duck! Rabbit! Duck!":
Daffy: Shoot me again! I love the smell of burnt feathers...and gunpowder...and cordite! I'm an elk! Shoot me! It's elk season! I'm a fiddler crab! Why don'cha shoot me? It's fiddler crab season!
Dogstar: Zeke, a malfunctioning robot who thinks he is a human, often strays into this territory. In "Rockin' in the Flea World", he chooses to ignore an alarm telling him that the Dogstar is flying into a black hole on the grounds that machines sometimes make mistakes.
Also qualifies for Daffy in his portrayal of Duck Dodgers in which said character has many a glaring example. One especially prominent one is when Dodgers decides he doesn't want to wait for the cadet to prepare blowfish and prepares it by slapping it around for a bit before taking a big bite out of the raw, unprepared blowfish with a 100% guarantee of it still being fatally poisonous.
Don't worry he only goes trippy for a while, if it were any other show he'd be dead already.
Peter Griffin from Family Guy is a particularly extreme example, as demonstrated throughout the show's run. Gets a lampshade in an early episode where Brian tries putting out a fire, only to discover that the extinguisher is a prank item that sprays plastic snakes - which promptly explode, exacerbating the fire. When the family comes back, Brian angrily demands to know Who Would Be Stupid Enough to do such a thing; Peter responds "A man who cares enough about prop comedy to put his family at severe risk, that's who!" Justified in that the episode "Petarded" revealed that Peter has mental retardation.
Brian's now infamous temporary death is the result of standing in the middle of the street.
Subverted by Fry in Futurama. Fry is so dumb that he lacks a certain brain function that even inanimate objects are said to have; ironically, it is the exact lack of this brain function that serves as a highly effective defense mechanism against extremely dangerous threats (i.e. threats that seek to destroy the entire universe) that are capable of reading minds, rendering him entirely invisible and mostly undetectable to them. It often falls to Fry as the only person in the universe who can save it, because his unique ability to survive against these threats derives directly from his being Too Dumb to Live. However, it's later revealed, that he lacks this brain function (delta brain waves), thanks to having sex with the woman who turned out to be his own grandmother, as he so eloquently puts it.
Zapp Brannigan is another odd case. He meets all the requirements except that his stupidity rarely hurts him personally. Even though the danger would be as likely to kill him as would anyone else in all but a few of the situations he causes through his epic stupidity/incompetence he always survives through dumb luck and/or heroically leading a retrograde advance while everyone around him (aside from the rest of the main cast... usually) dies.
And let's not forget "That Guy", who, during the 1980's, suffered from a terminal illness called Boneitis. A drug company was about to come up with a cure, and what did he do? He arranged a hostile takeover and sold the assets. He ended up freezing himself until there was a cure, but when he was unfrozen, he forgot to cure it and died during a major business deal.
On Goof Troop, Goofy is this way several times, most obviously in the episode "Goof Fellas", where he mistakes The Mafia killing someone with a cement suit for tailors and starts talking to them, which ends up not only putting his own life in danger but also Pete's.
The page image is from the Disney short "How to Have an Accident in the Home". Donald as the careless, accident-prone protagonist is jabbing a knife into the still-connected and operating toaster while complaining "confounded infernal contraption", immediately before the inevitable ZAP and electric fireworks. Donald also appeared in "How to Have an Accident at Work", pointing out accidents caused in the workplace due to carelessness.
It is amazing how long the eponymous character of Invader Zim has managed to survive, considering how often his idiocy has made things literally blow up in his face. GIR is a more extreme example, although being a robot, he's easily repaired.
Dib's sister Gaz seems to know about the aliens, and has used their technology or helped save the world (grudgingly) before, but the thing is though she knows the truth, she just doesn't care. In fact, in one episode she outright states she doesn't give a damn what Zim is doing because he's way too incompetent to do any damage.
Buckley from King of the Hill is a literal example of this. After ignoring Hank's advice on how to handle propane tanks (despite the fact that Hank has had years of experience), Buckley manages to blow up himself and the Mega-Lo-Mart.
This. That's right, Mega Man just took a bullet for a statue. Said statue was that of Abraham Lincoln, so it's partially justified.
The Powerpuff Girls' Mayor of Townsville. This even gets a Lampshade Hanging in an episode where the girls get sick of "saving the day" which as revealed turned out to be mostly mundane tasks like screwing in a lightbulb, at which point they decide to take a vacation. But they can't get a break, having to walk the town through defeating a monster.
Robot Chicken parodied The Hills Have Eyes by putting three of the dumbest celebrities together. One of them drove the car off the road when he complained things were "too hard" and claimed the tires were flat. The other complained to the main dumb idiot that she was just jealous that she got Aaron the dumb driver and that things were also "too hard." Both idiots left in a huff. Finally, the third idiot couldn't get back into the car, and realized either the dumb blond or the dumb driver had the car keys. Instead of going after them, she decided to go the completely OPPOSITE way.
Another one is a Fraggle Rock parody, reenacting Watership Down. The Fraggles are so stupid, they think moving cars aren't a threat, they don't recognize obvious traps, and ultimately are killed off since they made their new home under an oil well.
To say that the Sealab crew being this is an understatement; they're Too Dumb to Save the World, as evidenced in the episode "ASHDTV" where they get a combination asteroid smasher and HDTV intended for Spacelab, and despite warnings of a giant meteor heading towards Earth, ignore the TV's asteroid-destroying abilities and keep on watching TV.
In any case, Homer can (and will) be as stupid as he likes for the purpose of the Halloween episodes.
In the 2011 edition, he decides to chew off his arm in order to reach his bag of candy, rather than wait twenty minutes to have his arm freed. He chews off the wrong arm. Then the wrongleg.
In the 2002 edition, he found a hammock that could clone him and ended up making many who were dumber than him. With the threat of Homer clones overtaking the USA, Lisa, in front of the real Homer, suggests the military lure all the clones over a cliff with giant donuts. It works. And when Marge is about to relax in the end, she learns her Homer is a clone. The real one was the first over the cliff.
Grimes is Too Dumb to Livedeconstructed. One could argue that he wasn't too dumb to live, he was driven insane with frustration because Homer was literally too stupid to survive day-to-day life, if it weren't for the fact that he's a cartoon; the character of Frank Grimes was designed to illustrate this concept. That's right, folks: Homer Simpson is Too Dumb for other people to Live.
Most of the adult cast from South Park is this, but Randy Marsh takes the cake. Drives drunk with his kid and friends, purposely gets into drunken fights in little league games, gets Finland nuked off the face of the planet, is responsible for the death of his daughter's boyfriend.... His stupidity risks himself and pretty much anybody caught in the line of his scheme.
He also gives himself cancer just so he can get medical marijuana.
At times, Eric Cartman as well (He shifts between being too dumb to live, and an Evil Genius). One notable moment had him filling his TiVo with stuff from the History Channel on the founding fathers, and building a device that drops him and the TiVo into a water filled kiddy pool and electrocuting himself so he can have a flashback. Somehow it worked.
In The Spectacular Spider-Man when Spidey apparently walks right into an ambush and gets pounded, Shocker uses these exact words to describe him. He's wrong though.
Spongebob and Patrick from SpongeBob SquarePants. Once, they were lost in the wilderness with nothing but a food supply, water, and a shelter. Patrick starts a fire… with the food supply! Spongebob tries to put it out… with the shelter, which then Is destroyed. Spongebob finally succeeds in putting out the fire… with the entire water supply. So, they've wasted their food, water, and shelter when they're in the middle of nowhere.
Patrick once ate a Krabby Patty that had raw sewage in it, and Spongebob once ate a rotten Krabby Patty complete with maggots and fungi.
In "A Life in a Day," Spongebob and Patrick did lots of stupid stuff. Among them: Patrick riding through a car crusher and Spongebob making Patrick (and Larry the Lobster) fly into Ripper Reef, a very spiky and deadly rock formation.
In fact, most of the characters can qualify for this. Squidward once drove a vehicle off a cliff, Mr. Krabs sold his soul to many ghosts (and Spongebob), and Sandy did lots of stupid stuff in "Pre-Hibernation Week" and "Squirrel Record" (like juggling a ton of chainsaws then throwing them everywhere).
In "Imitation Krabs," Plankton put a one-cent selfdestruct slot on the robot he was inside. Plankton sums it up perfectly: "This wasn't one of my better ideas."
The smuggler Gha Nachkt from Star Wars: The Clone Wars. You'd think the guy would be smart enough to not be rude to a psychotic, eight-foot-tall, cyborg who could use four lightsabers at once, like General Grievous, but apparently, he was not.
Clone ARC Trooper Echo is this in the season 3 episode "Counter Attack". He charges right to the shuttle they were supposed to protect, while a commando droid fires a turret at him and he takes cover under the shuttle, only to be blown to smithereens, taking away the group's one way ticket out.
In Street Sharks, the protagonists suffer this in a big way. A prime example would be in the first episode, when they hear from secondhand sources that their father wants them to meet him at an abandoned power plant. No reason is given for this, he just wants them to, apparently. They predictably get kidnapped and, one bout of Playing with Syringes and seeming death later, wake up in a river. From there, they decide to get lunch, instead of seeing the police about the guy with the dangerous mutants who kidnapped and experimented on them and heavily implied he did something equally nasty to their dad. Or, you know, go to the hospital and get checked up in regards to the unknown substances injected into their bodies. This trope seems to be genetic. The first episode also has their dad confront the Big Bad in a remote location at night, without telling anyone where he was going or bringing any means of defense. To the surprise of no one, this sets up for a perfect He Knows Too Much scenario, and leads to him being missing in action for the rest of the show's run.
The Super Friends episode, "Volcano," had the captain of an alien ship that crashes lands into an active volcano. Despite the fact the ship and crew is in dire peril sinking into the magma, he refuses to accept the help of native superheroes because they may be "dangerous."
Lois Lane in Superman: The Animated Series. She's put herself in danger multiple times, but at least usually she didn't know how dangerous it was or at least tried to take some kind of precaution. But in Target she's being targeted for murder. She knows how dangerous her unknown enemy is and she's actually under police protection. During a phone conversation with Clark she suddenly realizes who the attempted murderer is. What does she do? She sneaks off to confront them face to face. While Clark and everyone else still thinks she's under police protection. If it hadn't been for Luthor just happening to call Clark to give him a vital piece of information she would have been dead by the end of the episode.
April O'Neil in the 1987 version of TMNT. From season 2 onward, Shredder et al. know where she lives. Yet, despite being kidnapped constantly, she never moves.
In the 2012 version, Timothy, aka "The Pulveriser", who refuses to listen to the turtles when they warn him that exposing himself to the Kraang mutagen is a seriously bad idea. So he deliberately mutates himself... and becomes MutagenMan.
The 2012 version of Michelangelo plants him firmly in this territory for the same reason. Similar to Timothy, he exposes himself to a can of mutagen on purpose, which causes his already mutated cells to start breaking down and eventually run the risk of killing him, forcing his brothers to look for a cure. Donatello had even planted warnings on the can that it was too dangerous to use, but Mikey had only looked on one side of the can that didn't have any labels.
Teen Titans: Robin has just had a fight with a shapeshifter who can impersonate anyone. And then she pops up and is like, "Hi, I'm totally Hotspot." He gives her his communicator without questioning whether it's really his friend. This nearly leads to all of the Teen Titans being frozen (Never Say "Die").
Miko of Transformers Prime is often extremely foolhardy and reckless. She constantly sneaks off to join the Autobot's adventures despite not really being able to take of herself or help in anyway. She begins to grow out of this as Character Development sets in.
Starscream tries to assert his authority over an Insecticon which was big enough and strong enough to snap him in half, and smacks it to obeying him. The Insecticon does not oblige and would have ripped Starscream apart if not for Airachnid's arrival.
Earlier Starscream managed to let slip that he was the one who killed Arcee's partner Cliffjumper while as her prisoner. He JUST managed to limp away with his head intact.
The titular character of The Twisted Tales of Felix the Cat somehow manages to be this AND extremely genre savvy at the same time. He's always gullible and trusting enough to wander head-first into disaster, but always manages to get out completely unscathed (most) of the time.
Hank and Dean from The Venture Bros.. In fact, they truly are Too Dumb to Live: the show reveals that they have both died 14 times, mostly due to their own incredible stupidity. Describing them as "death-prone", their father keeps a few clones growing in the lab as a precaution.