Who Would Be Stupid Enough...?

"Agatha: This really is a Wulfenbach Ship? Marie: Oh, yes. It was remarkably easy to steal. But then (glancing at her husband) who would be fool enough to try? Oggie: Hey! Iz like hyu vife iz callink hyu a fool wit-out ektually -- Master Payne: You cannot possibly be as stupid as you act. beat Oggie: Ken if I vants to be!"

- Girl Genius, February 7th, 2007

If there's anything too stupid for even a single person to think of, it hasn't been invented yet. The characters stumble upon an unbelievable con, or see a television spot that makes particularly outrageous claims.

If anyone says "Who would be stupid enough to fall for that?" or anything like it, you can be almost guaranteed that we'll see The Ditz displaying signs that they are stupid enough to fall for that, no matter how obvious the Schmuck Bait. This is also useful for summoning The Ditz to volunteer to do the aforementioned stupidity.

If you don't want someone to do it, you are clearly Tempting Fate to say this.

In some universes, this is a very dangerous trope to invoke.

May be followed by a Gilligan Cut, Answer Cut, or Inadvertent Entrance Cue.

You may ask yourself "Who would be stupid enough to ask questions like that?" There's your answer.

Closely related is someone showing up unexpectedly and others refusing to be surprised. "Yeah! I know you did this! Who else would be crazy/stupid enough to do this!"

Sometimes it will be deliberately invoked by someone whose enemies know they're not that stupid and allow them to catch the bad guys off guard.

See also Schmuck Bait.

For the case when a character innocently mocks some action in the presence of someone who did said action, see Oblivious Mockery.

Advertising

 * An M&Ms commercial for the 2012 Superbowl featured a Brown M&M at a party with a few guys snickering at her. When she asks why, a girl explains that they think she's naked. She chastises the guys, explaining that her shell is simply brown and that only a fool would think that she would show up to a party naked. Cue Red barging in and saying, "Oh, so it's that kind of party!" He then pulls off his shell and starts dancing. Brown was not amused.

Anime and Manga
"Ranma: There's no such thing as a bathing suit which makes a person able to swim. There is no one in the world dumb enough that would believe such a thing! Akane: Hey! How do I look?"
 * In one episode of Eyeshield 21, Sena watches a TV program on his team's new secret player, and there's a bit where Hiruma, posing as Eyeshield 21, gives an "obnoxious tough guy" speech. Kurita tries to assure him "No one would take that seriously", but then we cut to Monta watching the same program, talking about what a jerk Eyeshield 21 is.
 * In the first season finale of Sailor Moon, the youma create an illusion of a captured Tuxedo Mask, which Sailor Moon rushes toward. After the trap is exposed, they create the same illusion again. Sailor Mars says, "Do you really think she's stupid enough to fall for it again?", only for Sailor Moon to prove that she is.
 * In the anime episode of Ranma ½ that introduces Gosunkugi, he digs a pit in an attempt to trap Ranma. Two unnamed students ask each other who would make such an obvious trap, and who would fall into it. Enter Kunō...
 * In the manga, Ranma says this when Akane wins a bathing suit that supposedly makes anyone capable of swimming like a pro Olympian just by wearing it. Shortly afterwards, it turns out that it really does work.

"Yoko: Unfortunately, we are that stupid."
 * A Badass version of this occurs when episode twelve of Tengen Toppa Gurren Lagann pits the crew against Spiral King general Adiane. The fight ends up with Adiane's mecha on the deck of Team Dai-Gurren's battleship. Adiane taunts them with the fact that they wouldn't be stupid enough to fire on her when they're so close to one another.

"O'Brien: There's no way he'll attack head on. Judai: Battle! Featherman, direct attack!"
 * A variation happened in Higurashi no Naku Koro ni where Satoko said that only Keiichi would be dumb enough to fall for her mud Pit Trap. Cue a mud-covered Rika crawling out of the ground.
 * Played with on Slayers, where Lina sees a trap and tells Gourry that he'd be the only one stupid enough to fall for it... then Lina herself manages to walk right into the trap about ten seconds later, after being Distracted by the Shiny.
 * Yu-Gi-Oh GX gives us the following lines

"Kyon: Who would ever believe that? Koizumi: I was hoping that you might."
 * The dub actually does one better, and changes the first line to "There's no way he's dumb enough to attack me."
 * In Dragon Ball, whilst going through Pilaf's castle to retrieve the last Dragon Ball, Goku, Bulma, and co. follow arrows through a maze—leading to them being trapped. Pilaf remarks that he couldn't believe there were people stupid enough to fall for that.
 * A variant appears in The Melancholy of Haruhi Suzumiya.


 * In the first episode of Dominion Tank Police, a Mook in a stolen prototype tank is confident he's escaped the heroine's older model by climbing an elevator shaft, because she'd have to be some kind of lunatic to fire straight up at him. They both end up buried in the rubble.
 * Mahou Sensei Negima's Spinoff Babies series Negiho has the girls trying to force out Konoka's "stalker" by doing annoying things to her (like Face Doodling and Tickle Torture). Off to the side, Yue wonders how stupid the stalker would have to be to actually show up for such an obvious trap. Cue Setsuna blasting the lot of them with her Shinmeiryuu techniques, Neck Lifting Asuna while shouting "What do you think you're doing to Ojou-sama!". She's quickly caught in a stalker-snare afterwards.
 * This is practically a Running Gag in Gintama whenever Hijikata would ask who would be dumb enough to (action), cue Kondo doing said action.
 * In Squid Girl, to demonstrate to Nagisa that Squid Girl isn't a threat, they give her a fishing pole with a shrimp as bait. Nagisa just finishes telling herself that there's no way an invader like Squid Girl would fall for something so obvious when she feels a tug at the other end of the line.

Comic Books
"Bystander: What are those hideous fiends? Ms. Exposition: Well, the Lizard is called Gosana, and the Bat/Reptile is called Kame-Komori. They're from a series of low-budget Japanese films from a small and seedy film company called Dorobo Studios. They were created as rubber suit monsters to sponge off the popularity of much better film franchises at Toho and Daiei Studios. Many hard-core aficionados say they're the worst giant monster films ever made, despite some tasty special effects. Of course, the films have almost never been seen since the sixties -- so only a total geek loser would even know who they are. (next panel) Atom: (inner monologue) Hey! It's Gosana and Kame-Komori!"
 * In Jeff Smith's Bone, Fone Bone evades a pair of rat creatures by leaping onto a branch over a gorge and saying "Those rat creatures would have to be pretty stupid to follow me onto this frail, little branch." [[media:1145143428186.gif|Three guesses as to what happens.]]
 * In Hsu and Chan, rival game designers Satoshi and Akira Yamamoto discuss how the only way for the Tanaka Brothers to stop them from stealing the game innovation of the century would be to plow through security, rush the stage, and physically smash their computer. Akira remarks that "No sane man would--" before realizing who he's dealing with. Cut to Hsu and Chan discussing their plan to plow through security, rush the stage, and physically smash the computer.
 * In Countdown to Final Crisis Monarch asks "Who would be stupid enough to take a shot at me?" Turns out that would be Superboy Prime, who proceeds to rip apart Monarch's costume, destroying the universe.
 * From The All New Atom: Ivy Town is being attacked by two movie monsters brought into the real world.

"Sam: It smells like some kind of high-tech waste material compactor. They'll never think we were so incredibly stupid as to hide in here. Max: That's right! Nobody's that stupid."
 * Inverted in one Sam and Max Freelance Police short story parodying Star Wars.


 * Happens a lot with Smiffy from The Beano.
 * There's a Simpsons comic where a truck driver is delivering a shipment of bunnies to Springfield petting zoo, and a panther to Springfield zoo. He tells Groundskeeper Willy (working at the petting zoo) that the rabbits are in the crate on the left, wonders if he should clarify which left he means, then reasons that no-one could mistake a panther for a rabbit. In the next panel, Willy is brawling with the panther, who apparently didn't take kindly to being fed carrots.

Fan Works
"Yami: Does anyone here really believe that guy is a ghost? Tristan: I do! Yami: Anyone besides Tristan? (pause) Tristan: I do!"
 * Occurs in Yu-Gi-Oh!: The Abridged Series, although not with the exact same words:

"Brisbane: You can't mean that you're about to step on that map! Yugi: No,I was just gonna leave. Brisbane: So you're stepping on the map, then? Yugi: No, I'm leaving. Brisbane: ... Step on the map. Yugi: Make me! Brisbane: Oh, come on. I'll be your friend. Yugi: Look, there's no way I'm stepping on any freakin' map! Brisbane: What if I told you there was candy inside the map? Yugi: You've got to be kidding me! I'd have to be an idiot to fall for-- Tea: Hey, candy! That sounds pretty good! Tristan: Yes, let's go get the candy! (cue Tristan and Tea dragging a protesting Yugi onto the map)"
 * And later:

"Yugi: Man, Duke! I can't believe you actually thought that crappy little dice game would sell! Joey: Yea, it was just a carbon copy of Duel Monsters! You'd have to be as blind as my sister to not notice the similarities! Tristan: (holds up dice) This is going straight up my nose!"
 * Also subverted in another episode of the same series, where you'd expect Tristan to follow this trope again:

Films -- Live-Action
"Dark Helmet: So the combination is 1 2 3 4 5? That's the stupidest combination I've ever heard in my life! That's the kind of thing an idiot would have on his luggage! (later...) President Skroob: What's the combination? Colonel Sandurz: 1 2 3 4 5. President Skroob: 1 2 3 4 5? That's amazing! I've got the same combination on my luggage!"
 * In Spaceballs, the villains' plot relies on them discovering the pass code to the defenses protecting the heroine's planet. Dark Helmet eventually manages to get it:

"Gambol: You think you can steal from us and just walk away?! The Joker: (deadpan) Yeah."
 * In It Takes a Thief, The Chick makes fun of her fellow thieves who got conned into buying useless stuff off of infomercials... and then immediately hides her useless bracelet.
 * Played straight by The Chechen in The Dark Knight Saga: "Who's stupid enough to steal from us?" Turns out, The Joker. Although "stupid" doesn't really factor into it. Try "supremely confident".


 * When the Nazis demand that Indy hand over the Grail Diary in Indiana Jones and the Last Crusade, Henry Jones Sr. laughs at the idea that they'd assume his son was stupid enough to bring it with him after he'd mailed the diary to him in the first place to keep it out of the Nazis' hands. Unfortunately, Indy didn't quite get the memo....

Literature
""No one would be that stu--" Susan stopped. Of course someone would be that stupid. Some humans would do anything to see if it was possible do it. If you put a switch in a cave somewhere, with a sign on it saying "End-of-the-World switch. PLEASE DO NOT TOUCH," the paint wouldn't even have time to dry."
 * Somewhat lampshaded in the Discworld novel Thief of Time:

"Any true wizard, faced with a sign like "Do not open this door. Really. We mean it. We're not kidding. Opening this door will mean the end of the universe," would automatically open the door in order to see what all the fuss was about."
 * Shows up a lot in Discworld, in fact. In The Last Continent:

"Lando: (On the subject of infiltrating Xizor's palace) Let me get this straight; you want us to wade through sewage to get into this place? Dash Rendar: Exactly what the guards would think. Who'd be that stupid? Lando: Us. Who else?"
 * In Harry Potter, Ron wonders what teacher would be dumb enough to fall for the trio's planned deception about why they want a potions book in the Restricted Section of the library, having apparently temporarily forgotten that Lockhart is their Defence Against the Dark Arts teacher that year.
 * In Storm from the Shadows, Admiral Byng says something to this effect, thinking that Michelle Henke and the Manticorans will not actually make good on their warnings to punish the Solarian aggression. It doesn't end well for him.
 * In Norman Spinrad's Alternate History novel The Iron Dream, the author analyzing the work of Meta Fiction around which Spinrad's story is framed notes that some fans may yearn for a decisive and iron-willed leader like the one depicted in the work of metafiction to save them from Soviet domination, but concludes that no rational person would ever stand such a clearly delusional, bloodthirsty tyrant. Considering that the in-universe author of the work of metafiction is Adolf Hitler, well, I think you see Spinrad's point.
 * In Shadows of the Empire, several of the good guys' common-sense violating tactics are cited to work because the opposition wouldn't expect anyone to try them in the first place. Lando eventually lampshades this.

""That's the problem with our opposition – they keep thinking nobody could possibly be as stupid as we are. Fools 'em every time.""
 * Later he does it again.


 * Michael gets hit with this a couple times in the Knight and Rogue Series. On one occasion his reason for being at the scene of a murder (following orders to meet someone in an unadressed letter) isn't believed because the law enforcement can't believe anyone, especially someone without legal rights who knows something shifty is going on, would be stupid enough to get framed with such an obvious trick.

Live-Action TV
"The Doctor: He's making it up. There's no weapons up there, there's no threat. He just invented it. Harriet Jones: Do you think they'll believe him? Rose: They did last time."
 * In the Doctor Who episode "World War Three", after Joseph Green delivers a speech about an alien threat with "massive weapons of destruction", the following exchange occurs:


 * Notably, the Russian dub replaced the last line with "Well, you did believe." Translated from Russian here, of course.
 * While we're at it, the British electing the friggin' Master as Prime Minister of the United Kingdom...
 * Justified in that the Master was using the sound of drums rhythm to semi-brainwash the populace into voting for him.
 * On Top Gear, while Richard Hammond and Jeremy Clarkson are discussing a car which (theoretically) generates enough down force to drive upside-down (on the ceiling of a tunnel) at speed. Hammond mentions that the car's manufacturers have found the right tunnel and the right speed but they can't find a driver. Clarkson immediately volunteers Hammond to do it.
 * Buffy the Vampire Slayer. Spike gets this all the damn time. In Season 3's "Lovers Walk", Cordelia asks: "What kind of moron would want to come back here?" Enter our drunken moron. In Season 4's "The Harsh Light of Day", when he becomes a series regular, Buffy herself foreshadows the next three seasons: "A guy dating Harmony dead. Must be, like, the most tolerant guy in the world." Enter the most tolerant guy in the world.
 * In the "Fans vs. Favorites" season of Survivor, the Black Widow Brigade (Natalie, Amanda, Cirie, and Parvati) run into a problem when the last remaining outsider, Erik, wins immunity which will force them to vote one of their allies out. Cirie suggests to Natalie that she try to get Erik to give the immunity necklace to her by telling him that he's annoyed them so much that he won't be able to get enough votes to win unless he makes some grand gesture to the jury, to which Natalie replies, "No one would fall for that. I mean, who would be that gullible?" Still, she doesn't have much of a choice, so she goes along with the plan. And it works.

New Media

 * Our daily spam-filter shows that apparently yes, many people still are stupid enough to make it worth the spammer's efforts.
 * If you look it up, you'll be able to find the reasoning behind this: Spammers can produce such a high volume that even if only one in a million of their targets buys, they're still making a profit.

Newspaper Comics
"Lucy: Say, you don't think Charlie Brown would try to steal home, do you? Patty: Never! Not even Charlie Brown would do anything that stupid!"
 * The following exchange is from a May 1960 Peanuts comic strip, reprinted in May 2007:


 * In the last panel, Charlie Brown is standing on third base, asking himself whether he should try to steal home. And he eventually does try, too... which works out about as well as Charlie Brown's ideas usually do.


 * The plot element was featured in the TV special Charlie Brown's All-Stars.
 * A variant occurs during a Story Arc in the comic strip Bloom County, where Bill the Cat becomes a televangelist and claims if people send him $50 million, the Lord will "call home" Jimmy Swaggert, Oral Roberts, Jerry Falwell, and Jim Bakker. In the last frame, Milo says "Wipe out the gang of four, eh? Who knows who would fall for such a seductive pitch!" just as Opus is rifling through a wad of dollar bills. (This was a parody of Oral Roberts' fund raising appeal claiming that God would "call him home" if he didn't get a certain amount of money in donations.)
 * In a FoxTrot comic, Jason asked every member of his family if they wanted to have a snowball fight with him. They each reply "Do I look like an idiot?"... until he gets to Roger, who says "Let me get my coat." before Jason can even finish the question.
 * In one Garfield strip, a TV-commercial is blatantly stating "Are you a complete loser without any taste? Then we've got the thing for you!". Cue Jon coming in the room: "Hey, I've got three of those."

Radio
"Seagoon: Who would be idiot enough... Who would be idiot enough! To be dressed up as a German Admiral, and thrown overboard from a submarine? Lew: Don't worry! Look, I got an idiot in this box here who's been specially drowned for the job! (box is opened) Eccles: 'ello folks!"
 * Any use of this type of question on The Goon Show is invariably a cue for Eccles and/or Bluebottle to show up. The audience will often start giggling in anticipation before the question can even be finished.

Video Games
"Haken: You don't get it, Aschen. This kind of stuff is what gets you a lady's heart! Hell, they might even take the reward to the Zeit Krokodil for us, just for the chance to meet me again. Suzuka: You're an idiot, Haken. No woman would fall for that stupid attempt at manipulation. Kaguya: Haaakeeeennnn! Eeeeeee!"
 * In Chrono Trigger, one of the earlier bosses is described as "basically invincible, as long as no crazed idiot gets the bright idea to run up and hack at the head with a sword." Guess how you beat it. Go on, guess.
 * Although you don't need to hit the head at all. It's just that in the first play through you can't do enough damage to overcome its Healing Factor.
 * You can also shoot it in the face with a pistol.
 * In Final Fantasy VII, when the player is told by a conniving thief to pull one of two levers. It obviously makes no difference which is pulled, as the party is captured and the materia not returned either way. But Thou Must!...
 * One town in Breath of Fire 4 is filled with traps designed to scare away intruders. Fall for one particular trap and you'll be told by an amused villager that "not even the animals are dumb enough to fall for that one!"
 * Endless Frontier has this exchange.

"Guybrush: Aw, come on. Who's absent-minded enough to lose TWO wedding rings? Pyrite Parrot: *Squawk* It's me, Guybrush Threepwood, Mighty Pirate! Guybrush: Shut up, you!"
 * The copy protection material (a joke newspaper) for Space Quest 5 has an advertisement that clearly invokes this trope: "Are you a complete moron? Do you anything people tell you to? That's great! Send a copy of all your banking information to..."
 * Lampshaded and parodied when Elaine gives Guybrush her wedding ring in Tales of Monkey Island Chapter 2: The Siege of Spinner Cay:


 * In Portal 2, GLaDOS's chamber features a back door labelled: "GLaDOS Emergency Shutdown and Cake Dispensary". Naturally, there's nothing to do but try to open it. GLaDOS can't believe it when you fall for it.

Web Animation

 * On Homestar Runner, Homestar himself usually fills this role. For example, in the Strong Bad Email "candy product", Strong Bad designs a chocolate bar in the shape of a pair of pants with a bite taken out of them "for security, 'cause who's gonna steal a pair of half-eaten choco-pants?" At the end of the cartoon, an Easter Egg features Homestar, dressed in Burglar Wear, finding one of said candy bars on the ground and remarking "Ooh, pay dirt! A pair of half-eaten choco-pants!"
 * In "record book", Coach Z attempts to set a record for "longest time singing the 'I'm Just Me' song while hopping on one foot with nine pieces of bubblegum stuck to your face". While Strong Bad is in the middle of decrying the record as "random crap that nobody would ever do", we cut to Homsar doing exactly what Coach Z described.

Web Comics
"Roy: This desert is so unbelievably large that anyone with more than two brain cells would know better than to try searching the whole thing. (a few panels later) Elan: OK, so how do we search the rest of the desert? Roy: Elan, I just said that anyone with more than two-... Elan, the desert is too big to search the whole thing."
 * This Narbonic strip.
 * This page of Order of the Stick:

"Kin: They were first created long ago by a wizard who hated trespassers. Now they grow wild in some areas. They're only a danger to the dumbest of individuals. (Kin and Forgath shares a look) Kin & Forgath: MINMAX! Minmax: (both legs sticking out of the carnivorous plant) MM! MMHMM! MMM!"
 * In Sluggy Freelance, Torg and Riff visit a space station in the Star Trek dimension, where Riff is warned that they must be discreet in this dangerous world. Riff replies that, "Discretion is our middle name." Cut to Torg shouting at a Klingon wielding the traditional blade, "No, YOU have no honor!"
 * This Penny Arcade strip, in which Tycho's niece Annarchy wonders what sort of "pea-brained monkey man" conventions like E3 are supposed to appeal to. Apparently, Gabe is one of those pea-brained monkey men.
 * Goblins gives us the Treasure Plants.


 * Girl Genius had a brief discussion between Violetta and Wooster about who could be crazy enough to hijack one of Her Majesty's sub-hunters, all on his own at that. It turns out Wooster knows a guy like this.

Western Animation
"Leela: I wonder why Dr. Zoidberg is acting this way. Out of all of us he always seemed the most normal. Zoidberg: (with rubber bands holding his claws shut) I am normal. Amy, take off these rubber bands and I'll show you how normal I am! Amy: (whose clothes have been ripped and torn) Fool me seven times, shame on you. Fool me eight or more times, shame on me. (later...) Amy: (holding two rubber bands) Dr. Zoidberg said I should hold these while he's gone. Bender: (Face Palm) Zoidberg: (warbles ferociously) (everyone else screams in terror) Bender: Moron!"
 * In an episode of Garfield and Friends, Garfield gets a TV fitness guru kicked off the air by using cue cards from other shows to trick him into doing ridiculous things on camera, like wearing a dress and hopping on one leg while honking like a goose. As Garfield heads home, he asks himself "Who would be stupid enough to do all that stuff?" Once he gets home, he finds his dimwit owner wearing a dress and hopping up and down on one leg while honking like a goose.
 * Throughout the series, Odie has repeatedly made his first appearance in an episode after the use of this trope, to the point that Garfield began lampshading it. "Six seasons and he's never missed a cue." Also lampshaded in a segment on comedy method, where at one point, Garfield talks about comedy timing, and demonstrates by using some variation on this trope, followed by Odie jumping in, with some kind of costume.
 * However this is subverted at one point, when Garfield asks who would be dumb enough to be out in the middle of a blizzard... and Odie appears right beside him, causing Garfield to comment that not even he was stupid enough to be out there.
 * In the episode "Why Must I be a Crustacean in Love" of Futurama, the following exchange occurs, after Zoidberg has gone berserk in a New New York City health club:

"Leela: Who buys this crap? Bender: Idiots who need gifts for other idiots. (Fry walks in from off screen, holding two moon-themed T-shirts) Fry: Hey, look what I got you guys!"
 * Also, in the episode "The Series Has Landed", while they're at a theme park on the moon and browsing the souvenirs:

"Fry: What kind of bozos would start a Bender protest group? Prof. Farnsworth: Good news everyone, Hermes and I have started a Bender protest group. Zoidberg: That was uncanny!"
 * And again in "Bender Should Not Be Allowed on Television":

"Ratchet: You're gonna destroy the city! You wouldn't dare do something THAT stupid!! Wreck-Gar: I am Wreck-Gar! I DARE to be stupid! I WILL DESTROY THE WHOLE CITY!"
 * In the Teenage Mutant Ninja Turtles 1987 episode "Super Rocksteady and Mighty Bebop", Shredder complains to Krang when Krang's mind control device makes its victims act like children instead of becoming willing slaves, and Krang protests "only a complete idiot" would invent something like that. As he realizes what he'd just said ("A complete idiot?"), he hollers at Rocksteady and Bebop, who sure enough had earlier accidentally damaged the device without telling their bosses.
 * Family Guy hung a Lampshade Hanging on this trope in the episode "Too Sexy for His Fat," in which Lois responds to Chris's decision not to undergo liposuction: "That was a very grown up decision! I mean, what kind of lazy, narcissistic, irresponsible moron would even consider doing something as unbelievably foolish as getting liposuction? Who, I ask you? Who?" This line is immediately followed by the appearance of a newly svelte Peter.
 * From the Transformers Animated episode "Garbage In, Garbage Out":

"(Megatron, Starscream, and Lugnut currently on board Omega Supreme without any weapons) Starscream: (to Shockwave) Lucky you! Meantime, we get to float up here and get picked off by the Cybertronian Defense cannons! Megatron: No Autobot would be foolish enough to fire on their greatest weapon. (cut to Autobot Council meeting) Sentinel Prime: I say we fire on Omega Supreme!"
 * And from "This is Why I Hate Machines":

"Bumblebee: Who'd be crazy enough to volunteer for that mission? (beat) Why's everyone looking at me? Why's everyone always looking at me?"
 * This happens at least twice to Bumblebee in season one ("You mean they actually sell spare parts on the open market? What kind of malfunction would be crass enough to buy this stuff?), and he does it to himself in the Grand Finale.

"Homer: Yeah, they pulled it off the market when they found out it was toxic. But I figure, if you're stupid enough to eat it, you deserve to die. BART! Bart: (spraying Funny Foam into his mouth) What?"
 * In The Simpsons episode "Homer's Barbershop Quartet", we learn that his band's picture was put on a can of something called Funny Foam.

"Lisa: There are a lot of religious watchdog groups out there keeping the world safe from the horror of free expression. Bart: You mean there are losers who spend all day watching TV looking for stuff to complain about? Who'd be lame enough to do that? (cut to Flanders doing just that)"
 * "You said 'no one's dumb enough to pay a twenty dollar processing fee'!"
 * Also from "You Kent Say What You Want"

"Vincent van Ghoul: Don't worry, only a complete dimwit would open that chest. Daphne: Speaking of dimwits, where are Shaggy and Scooby? All: Uh-oh..."
 * The pilot to The 13 Ghosts of Scooby-Doo:

"Harvey Bullock: Maybe she went down the laundry chute. Dr. Leeland: None of these yahoos are crazy enough to pull that old stunt. Poison Ivy: (in her cell and upon hearing this) Ha! (cut to Harley Quinn in a washing machine) Harley Quinn: Help help! Ivy! Anybody! Get me out of here!"
 * Invoked by Don Karnage in Tale Spin.
 * In the "Joker's Millions" episode of Batman the Animated Series, Harley Quinn finds out that Joker has replaced her, and decides to escape from Arkham to get her revenge. When they realize she's missing, the following exchange occurs:

"Phantom Limb: No one "retires" from Phantom Limb's shit list!"
 * In The Venture Bros Season 3 premiere, we learn in a flashback that The Monarch used to work as Phantom Limb's henchman while moonlighting as The Monarch and seduced Dr. Girlfriend during this period. When Phantom Limb catches them in the act, he doesn't recognize him (as he's off uniform) and demands he identify himself. The Monarch then makes up the name "Manotaur" on the spot after looking at the big "M" on the hood of the Monarchmobile. Phantom Limb is then summoned by the Council and before leaving tells "Manotaur" he is now on Phantom Limb's "shit list". The present Dr. Girlfriend, who is learning of this via video footage, claims it's impossible that Phantom Limb (probably the most competent and intelligent villain on the show) would be stupid enough to fail to recognize his own henchman. In the episode's epilogue, we see Phantom Limb descending on a retired, completely innocent, and looking-nothing-like-the-Monarch Manotaur...

"Azari: There's no-one here. Maybe Ultron assumed no-one would be dumb enough to sneak in. Pym: HA! We showed him! We are dumb enough!"
 * In Next Avengers: Heroes of Tomorrow, when the gang infiltrates Ultron's base:

"Lucy: I've never seen it rain so hard for such a long time. Linus: I'm just glad I'm inside. Lucy: Well, good grief. Only a real blockhead would be out in a rain like this. (cut to Charlie Brown standing on the pitcher's mound) Charlie Brown: Where is everybody? We're supposed to have a ballgame today!"
 * In the Peanuts special Charlie Brown's All-Stars, Linus and Lucy are looking out the window at a heavy rainfall:

"Mr. Plotz: There must be someone who can deliver this stuff / But where can I find someone stupid enough?"
 * In the Animaniacs version of The Night Before Christmas, Thaddeus Plotz says exactly this about Ralph the Guard when deciding who should deliver presents to the Warner Bros. (and Sister):

"Frylock: (reading e-mail) "Go down to the park and step into the rainbow and you'll be rich with gold. Forward this to 20 people or we will burn your brain from the inside. Go down to the damn park." Man, who would be stupid enough to check this out? (cut to Carl, waiting at the park) Carl: All right, I'm gonna give this rainbow thing another five minutes, and if it doesn't show up quick, then I am going down to the store and get a hot-rod magazine. (They got the chick with the boobs.)"
 * In the Aqua Teen Hunger Force episode "Escape from Leprechaupolis", Frylock receives an obvious scam in his email.

"Cameraman: Naw, come on. D'ya really think anyone will fall for somethin' that stupid? Cartman: Six hundred dollars, you guys! Come on, get your stuff together!"
 * Used indirectly on Invader Zim. The episode "Bad Bad Rubber Piggy" opens on an episode of Professor Membrane's show about time travel. After demonstrating the consequences of time travel, Membrane proclaims "anyone who would build a space-time object replacement device is a complete moron!". Guess what Zim's doing at that exact moment?
 * In the Beach Episode of Jimmy Two-Shoes, when seeing people dancing on TV, Heloise mutters "Who dances like that?" in a clearly condesending tone. Naturally, Jimmy and Beezy provide the answer.
 * Lampshaded in an episode of American Dad ("Finances with Wolves"). The family is in a mall and Hayley is griping about the consumerism run rampant. She asks what kind of idiot would buy into all this; Steve sighs heavily and says "And we widen to reveal...", at which point Stan enters the scene covered in useless junk (and a jacket made of money).
 * At least once, the narrator would ask "But who would be stupid enough to [plot contrivance]?" as a lead-in to an entry by Bullwinkle - "I would!"
 * In the South Park episode "The Tooth Fairy's Tats 2000" the kids are running a tooth racket where they collect the money from under other kid's pillows. A sting operation is set up to catch them in the act, with a news report about a kid getting $600 and his exact location.

"Sparky: You really don't think Maximus is stupid enough to open that chest, do you? [Maximus' ship explodes] X5: Yes, apparently he is stupid enough."
 * In Transformers Generation 1, the Quintessons bargain for their lives when Galvatorn barges onto their ship, one of them saying, "If you destroy us, you'll never find the Decepticon Matrix!" (This is a bluff; an Evil Counterpart of the Autobot Matrix of Leadership does not exist.) Another of the Quintessons whispers to the first one their own version of this Trope, "I calculate a 77.9% chance he doubts the existence of a Decepticon Matrix". He overestimates Galvatron's intelligence; he quickly demands they tell him where it is, enabling them to send him and his men on a wild goose chase.
 * Happens in an episode of Atomic Betty after Maximus steals a decoy treasure chest:

Real Life

 * The origin of the term "Murphy's law".
 * The concept behind The Darwin Awards which collects such stories that result in death.
 * Or removing themselves from the gene pool through... other methods.
 * Hannibal's march over the Alps into Italy. The Romans were caught completely flat-footed by it because they didn't think anyone would be stupid enough to try.
 * In fairness, even he lost a not insignificant amount of his army in doing so, so the Romans were somewhat justified in their belief.
 * Likewise the Nazi conquest of France in 1940. The French left hardly any troops covering the Ardennes sector... because no one would be stupid enough to try and launch an attack through such rough terrain. As with Hannibal, it's not that they were stupid enough to try something impossible; it's that they were good enough to make it possible.
 * The fact that the Allies left almost no troops there when it was recaptured in 1944 allowing the Nazi's to do the same thing again does makes the Ardennes a case of the Allies being Too Dumb to Live as well.
 * Charles XII of Sweden's invasion of Russia. Napoleon's invasion of Russia. And later, Hitler's invasion of Russia. Hint: do not start a land war in Russia.
 * Especially when it's winter in Russia (as was the case with Hitler).
 * Actually, he started the invasion in June. It took longer than expected. The Nazis actually expected to launch their attack on May 1, but had to delay for six weeks to conquer Yugoslavia. Many historians speculate that the extra six weeks of warm weather in Russia might have resulted in victory.
 * And never go in against a Sicilian when death is on the line!
 * Only one man has actually successfully conquered Russia. That was Batu Khan (who was almost as Badass as his grandfather Genghis). And Russia wasn't united at the time.
 * Though by not being dumb enough to try in the middle of another war anything more than a short campaign to punish princes who killed his ambassadors. Being strong and unobtrusive made Horde attractive, so when the prince of the richest Russian city had to choose whether to deal with them or the Crusaders, he bothered to travel all the way to Batu and became his son's "blood brothers" to join as a client-state.
 * Somehow, people are still falling for the Nigerian Scam.
 * Ditto for diploma mills—phony universities that thrive on the USA's legal voids and loopholes, which sell diplomas without even teaching anything. Google about "diploma mill" and you'll see many stories of people who actually believed they were now experts in computer science after buying their diplomas without even studying anything, who were shocked beyond belief when they found out their diploma was rendered null and void after the "university" was raided.
 * Who would be stupid enough to launch an invasion of Finland during a harsh winter, while deliberately not using any soldiers from similarly cold regions near the Finnish border (out of paranoid fears that they'd be too sympathetic with the Finns)? Josef Stalin, that's who. The result was technically a Soviet victory, but only through overwhelming the Finnish defenses through sheer numbers. As one Soviet general put it, "We have won enough ground to bury our dead." This embarrassing performance against the vastly smaller and more poorly equipped Finnish Army, incidentally, was a major factor in Adolf Hitler thinking he could duplicate Batu Khan's feat of conquering Russia. (He couldn't.)
 * Stalin himself invoked this trope almost word for word when aviation minister Mikhail Khrunichev and aircraft designer A. S. Yakovlev proposed to buy advanced jet engines from the British. "What fool will sell us his secrets?" At the time jet engines were revolutionary technology and selling them would be the equivalent of selling stealth technology to your worst enemy today. Turned out the British Labour government was that stupid. They sold the Rolls Royce Nene to the Soviets who put it in the MIG 15. The Mig gave air superiority to the North Koreans during the first stages of The Korean War, before the appearance of the F-86 Sabre. Just to add insult to injury, they never paid the British the licensing fees either.
 * Battle of Leyte Gulf: The Japanese Navy's "Shō-Gō 1 Plan" was for a decoy fleet, the Northern Force, to get the attention of the US Navy's covering forces and draw them away so that their Center and Southern Forces could attack the American Landing Zones at Leyte Island. William F. Halsey, commander of the USN 3rd Fleet, fell for the ruse by speeding after them with all of his ships, leaving a handful of Destroyers and Escort Carriers at the mercy of attack by Takeo Kurita's Center Force which occurred near Samar Island.