"I'm the caster, y'know! It's like I'm a cannon made out of glass. Like a... y'know, like a dainty figurine so ornately decorated you can't imagine how something so fragile manages to exist in this brutal, ugly world... And it makes you weep."
If it weren't for their Healing Factor, the Titans in Attack on Titan would be incredibly easy to destroy. Sure they're huge and if they grab you you're dead, but their bodies are incredibly light and fragile. This is especially true of Eren, who often hits things so hard, his bones actually snap apart from the impact and have to regenerate. This is best showcased when he punches a Titan in the head so hard, its head is sent flying into a church, but his hand is destroyed in the process.
Fate's Sonic Drive form introduced in Magical Girl Lyrical Nanoha Strikers. It improves on her original Sonic Form by giving her a lot of oomph to complement the speed increase, boosting her magic powers to astounding levels and letting her access Bardiche'sRiot Zamber form. But much like the original Sonic Form, all of this comes at the cost of armor, so all it'll take is one good hit to make her fall. Not that it proves to be much of a detriment; so far, only Erio has managed to land a hit during a mock battle in Magical Girl Lyrical Nanoha ViVid, where it indeed wiped out most of Fate's Hit Points.
Hayate has also shades of this: her spells range from nuclear explosion to... bigger nuclear explosion, but it comes with looooooong casting time and inability to take hits. She even said Caro would win against her in one-on-one. This is counterbalanced by the fact that Hayate almost never fights one on one; even without her other allies, most of the time she still has Reinforce with her, who can separate and hold off a target with a slew of not quite as powerful, but quite a bit faster spells while Hayate prepares her Wave Motion Gun.
Lutecia Alpine is an S-rank summoner who, in StrikerS, is capable of summoning insects that rival Caro's powers, but has hardly any moves with which to protect herself. However, as of ViVid, she appears to have developed the magical capabilities to fight alone well enough to enter the tournament alongside Vivio and her friends.
The Numbers from StrikerS are very powerful, but they can't take hits that well and most of them seem to not have defense skills. Their teamwork makes them dangerous, but if you're strong or skilled enough to take one after another down, then it's not a problem. In the Grand Finale, all Numbers are defeated by one or a few hits.
Like Fate, Micaiah Chevelle from ViVid is this overlapped with Fragile Speedster: she has a Barrier Jacket (or Knight Clothing) which is designed to give her immense speed for minimum defense. This speed supports her extremely powerful sword attacks greatly, but her lack of defense becomes a lethal disadvantage against Lightning Bruiser Miura who has melee versions of Nanoha's Starlight Breaker.
The Big Bad of the final arc of Ranma ˝ has powers bordering on a Person of Mass Destruction and he can tank Ki Attacks, but a rather pampered life has lead him to be rather weak against physical attacks. Of course this is just compared to the completely Made of Iron fighters in most of the series (he was called a wuss for being moderately injured by a boulder... being thrown by tornado winds that were drilling into the ground and altering the course of an underground river).
Akane Tendo as well. Though she can dish out punches with the best of them, she has nowhere near the healing speed or toughness of any of the other characters; while she is too skilled to be The Load in an actual fight, she is still regarded by some as a Damsel Scrappy because she insists on getting into a fight, but somebody (mainly Ranma) usually has to keep an eye on her because she can't take the hits they can.
Pikachu fits this trope well in Pokémon. Massively powerful attacks? Check. Tendency to go down quickly in a fight? Oh yeah.
Tieria Erde's Gundam in The Movie, the Raphael, is this. It is equipped with Big Friggin'Wave Motion Guns that can also function as Attack Drones. However, due to said Gundam not being equipped with real GN Drives as well as the lack of resources used while it was being created, all defensive capabilities were sacrificed in favor of its offense. His earlier Gundam Nadleeh qualifies as well: it's essentially a Fragile Speedster with the Exia's close-combat attack power. Naturally, it's only used in emergency as it's a Dual Mode Unit, its other form being Gundam Virtue.
The GN Arms from the first season too. Lockon absolutely owned everyone with it until Ali incapacitated him with a single well-aimed shot at his beam cannon. Then it turned out the Gundam piloting the exoskeleton is tougher than the actual exoskeleton! Another example of this trope is the Gadessa: its main weapon is a Wave Motion Gun with ridiculous range... and not much armor. It still has a backup weapon and a beam saber but its defensive capabilities are nowhere near those of the others, as Lockon took it out in the final battle with a point-blank burst from his Gundam's sidearm afterPlaying Possumto lure it close.
Even seen in Mobile Suit Gundam MSIGLOO during the gravity front. Zaku's are portrayed as having tremendous and devastating firepower...but one direct hit from a tiny tank or missile team can still one shot them. Fortunately it seems that even non new type mook Zeke's can Dodge the Bullet.
Lillidan Crauser of The Prince of Tennis. He is extremely powerful, able to curb-stomp a bloodshot Kirihara using even greater violent play than him. However, he lacks stamina and defense.
In Hajime No Ippo, minor character Eleki Battery who fought Kimura is definitely one. He has enough power to knock Kimura down in one blow, however, all Kimura needed to do was land one hit to his body to knock him down.
Also Ryuichi Hayami, who's got very good counters and speed as well as strength... but one well placed punch and he's out. This gets so bad that, when Kobashi manages to deal him a REALLY well-placed hit in the jaw, the injury he sustains forces him to retire.
The Japanese National Team in Captain Tsubasa. They've got excellent scorers in Tsubasa, Aoi and Hyuga as well as great GK's like Wakabayashi and Wakashimazu, but one of their biggest flaws is how easily their defense can be torn and the rival teams can try their luck at scoring. And since the two Waka GK's are prone to Game Breaking Injuries...
Single player version: Jun Misugi. Excellent strategist, very dedicated, great at teamwork, marvelous scorer... and with pathetic stamina due to being an ex-Ill Boy. Hence why he's seen more often than not in manager positions and doesn't play until it's mandatory.
Similarly, Hisashi Mitsui from Slam Dunk is one of the best 3-point scorers in Japanese HS basketball. But around 3/4 of an intense game, he's almost completely knocked out and unable to merely walk outside the basketball fields.
In the first season if Yu-Gi-Oh! (where the card game was the least like its Real Life equivalent) both Zombie and Machine-Type Monsters were described like this, incredibly strong on offense but really bad at anything else, especially defense. (Of course, the actual game isn't like this at all, at least not all the time.)
Nami from One Piece. Her Clima Tact can make very dangerous lightning attacks, and while they take some time to charge up, her offensive power with these makes her one of the most dangerous Straw Hats. She is one of the very few people who can hurt Luffy with a regular punch, though it is because she "beats up his spirit". Her durability, however, is very puny and no better than that of real life human.
Early series baddie Kuro is this as well. He can slice people up like Salami, and his Shakushi ability makes him damn near untouchable. However, he just can't take a hit. When Luffy slows him down, the fight ends very soon after.
May of Fullmetal Alchemist has quite a few different ranged attacks with her alkahestry, but is one of the least durable characters, partly the result of being a young girl.
Alyssa of Mai-Hime has the ability to cause devastation on a large scale with her Child, Artemis, but unlike other Himes, does not have an Element to protect herself, instead relying on Miyu's assistance.
Shin Kazama of Area 88 fits this trope. He deals a nasty blow to Saki's head during a temporary psychotic rage, but Mickey floors him with one punch.
Itachi Uchiha is basically this in Naruto. Despite having three of the most powerful attacks in the entire manga, Itachi's base arsenal lacks versatility. Not only that, a sufficiently strong character could One-Hit KO if they got close. His stamina is particularly low as well, meaning he can't fight for extended periods. Those three powerful attacks? They cost more than 30% of his total chakra, meaning he can't spam them like his brother Sasuke can.
The Grand Cross from Bodacious Space Pirates can be considered as an example of this. It possesses advanced technology and high-tech weapons that can destroy spacecraft instantly. However, its shielding is very vulnerable to heavy bombardment.
Space Battleship Yamato has the Super Battleship Andromeda. All the ships in the Andromeda fleet have double wave motion guns but still get easily destroyed just by the force of the White Comet's vortex.
In The Legendary Moonlight Sculptor, the main character Weed considers his non-combat title-class to be this, he calls his class a "glass sculptor" as his unique attacks do a lot of damage, but because he is a crafter class, he cannot equip heavy armor, and does not receive the ordinary damage reducing skills of, say, a warrior.
Ikkaku's zanpakutou is unpredictable, dangerous and incredibly powerful. However, it breaks easily because the shikai is wooden and the bankai's overpowered force makes itself brittle. There's a heavy implication that his zanpakutou breaks so easily because Ikkaku is refusing to use his power correctly. Ikkaku himself is not this trope.
Ran Tao in the anime filler Bount Arc is a very skilled kidou user but her stamina is heavily compromised by her extreme age.
There is an old (board and miniatures) gaming expression called the fuzzy wuzzy fallacy (after the Rudyard Kipling poem). Basically it states that a unit's effectiveness goes up proportionate to the square root of any increase in firepower (provided the defense stays the same). For example, the above Mech has roughly 3.5 times the firepower of the old version. FW numbers say that it's about 1.87 (the root of 3.5) times as effective as the old one, given that both die just as easy (and will draw fire like no-one's business).
In the Flying Frog game Touch of Evil, the schoolteacher only has three hit points and no healing factor. However, loading her inventory up with books adds two additional fight dice per book. Collecting all the books on the board gives her three hit points...and up to twenty dice's worth of damage.
Many telepaths in X-Men, such as Professor X, have powerful Psychic Powers but very weak physical attacks, and aren't of much use against opponents immune to telepathy (like robots).
Similarly, Cyclops' Eye Beams are devastatingly powerful, but if anyone actually hits him he's just as vulnerable as any non-powered human. Well, any non-powered human in peak physical condition with iron willpower and light body armor, but still — a lot of X-Men fight scenes start with Cyclops getting punched out or shot with regular bullets, because (from a writing perspective) otherwise he could settle the whole business with a look.
And, Storm may have god level power, but up close, she's hard to hit, but just as easily hurt as anyone else. Same with most of the other X-Men whose specialty is offensive power.
The same is true of Marvel magic users like Doctor Strange, Scarlet Witch, or Wiccan. They can do frightening things to time and space with little more than a gesture and some concentration, but they can also be rendered helpless by a Tap on the Head, drugs, being overwhelmed by bodies, being distracted in mid-spell, or simply being Bound and Gagged.
Much like the X-men with offensive powers is Fantastic Four member Human Torch. His flame powers give him move high movement speed and an offensive edge. Unlike his allies he lacks any way to use his powers to defend himself other than flying out of the way.
Humpty Dumpty in the FablesSpin-OffJack of Fables is an almost literal example, being a cannon that was bowdlerisation into being an egg man.
Zatanna of The DCU can kill people with a (backwards) word (not that she ever has, she is a superhero). Only the stronger magical, divine, or cosmic beings in the DC universe can resist her powers. However, she isn't any more durable than most humans and can be taken down with a single well-placed punch. Overlaps with Squishy Wizard. In Identity Crisis it is even explicitly mentioned in the narration-bubble: She is the most powerful member of the team, if she can get the words out. Slade Wilson (Deathstroke the Terminator) pokes her in the stomach, so lightly that it does not even hurt that much, but once she begins to vomit from the damage to her liver she is out of the fight.
Prism, an on and off member of the X-Men villain Mr. Sinister's Marauders, is literally made of glass. He can store light and energy (such as sunlight or Cyclops' optic blasts) and redirect it to devastating effect. But he is still made of freaking glass. Jean Grey killed him once by throwing him into a wall (not even that hard).
The Spider-Man villain Dr. Octopus may have control of four powerful and deadly metal arms, but he's otherwise a normal, somewhat out of shape human. Once the super-strong Spidey gets past his formidable defenses, Doc Ock goes down pretty quickly.
In An Entry With A Bang!, the marauding pirates with their Battletech... uh, tech... are somewhat confused by the fact that while Clancy-Earth has highly effective BVR capability, their warmachines can't take hits worth a damn.
The Firefly fanfic Forward puts an emphasis on River being one of these; she's portrayed as fast and powerful, but one good hit puts her down, which happens several times in the story.
Lightning Bolt is one of these in Ace Combat: The Equestrian War. She is the only pony of the main heroines to have a powerful special attack (Shining Spark), but she is prone to being injured during prolonged battles.
Devastator in The Measure Of A Titan is practically the paragon of this. His powers are theoretically capable of splitting a planet in half, and he can use them to fight multiple high-level metahumans at once, but he is as fragile as any normal human, and heals as slowly also.
Battleship correctly shows that modern-day missile destroyers are this. They carry lots of missiles and the Aegis system allows them to Macross Missile Massacre an enemy, but they lack any real armor to protect them from return fire. The CIWS guns do an admirable job trying to protect the ships from the alien attack, but the enemy employs the More Dakka tactic to overwhelm the defenses.
Katniss of The Hunger Games is a quickdraw with a bow and takes out several competitors in seconds. Compared to the opposition she is untrained in how to fight up close and is slowed down significantly by relatively minor injuries.
Star Wars has TIE Interceptors, whose armament - twice or even occasionally thrice that of the more widespread TIE Fighters - means they actually represent a threat... for a short while. Their shielding is no better than that of the Fighters (that is, none whatsoever), so they break apart as soon as someone shines a laser pointer at them.
In Phoenix Wright: Ace Attorney, the flashback to the DL-6 incident shows that young Edgeworth was able to bite Yanni Yogi hard enough to distract the baliff from hitting his father, and later threw a gun at him hard enough to knock the guy out. When Yogi shoves him hard enough to be knocked against a wall though, Edgeworth collapses almost immediately. Given that he's a kid, it's pretty justified.
In Pacific Rim, the Japanese Jaeger, Coyote Tango, has huge retractable cannons mounted on its shoulders, but is apparently the most lightly armored of the Jaegers.
In The World's End, the Blanks have inhuman strength and agility, but you could burst their heads open with a well-thrown punch. This probably explains why our heroes, a bunch of a middle-aged out-of-shape men, are able to deal with crowds of them.
In The Dresden Files Harry mentions that wizards are like this; for all of the magical weight they can throw around, they still need all of their squishy internals to work. Harry reasons that instead of being on the defensive, he should punish the other wizard in their back-alley duel. When dropping a car on the guy doesn't work, Harry realizes that he's boxing way out of his weight class. The guy in question is the current most likely candidate to being on the Black Council.
In Honor Harrington there are several ships like this. At one end of the extreme are outdated Solarian Navy ships which put more focus on offensive weapons than counter missiles and point defense lasers. Likewise, Maya's Arsenal ships which are capable of carrying thousands of long range missiles, but are just converted freighters and have no defense at all.
Special mention to HMS Wayfarer and her sisters: converted freighters, sluggish and armored for crap, but carrying super-dreadnought-class main guns capable of carving up a battlecruiser like a roast turkey, a complement of light-attack craft capable of laying down significant hurt in their own right, and, oh yeah, the first roll-out of the Manitcoran Missile Massacre.
Honor's first cruiser, the HMS Fearless was refitted with weapons that would allow it to kill far bigger ships. But the weapons' short range and the lack of any decent defenses resulted in a single resounding success during the first fleet exercise, and getting 'destroyed' in every exercise thereafter once the opponents had realized the threat and decided to give some payback for the first success.
The Manticoran LACs introduced in Ashes of Honor are armed with battlecruiser grade grasers, but they're not very survivable should an opponent decide to focus on them. In universe, LACs in general are described as "eggshells armed with hammers".
Not surprisingly the Lensman universe plays with this one, but the vulnerable sluggers are always accompanied by copious numbers of their exact opposite - ships that are all shield and nothing else (sometimes not even a human crew). There are, however, usually large numbers of balanced ships in the same fleet.
In the Bolo books, there are Enemy units that are just counter-grav platforms mounting Hellbores. They can be easily swatted by said supertanks, but can be a problem if allowed to attack. They aren't One-Hit Kill-capable, but the numbers are always on their side.
Coinshots in Mistborn are a kind of Misting who have only one power: the ability to telekinetically shoot metal away from their bodies. This makes them able to dish out a ton of damage, since a Coinshot with a pouch of money is basically a human machine gun, but they have no greater ability to resist damage than anyone else. Have a half-dozen Coinshots protected by about the same number of Thugs (Mistings who can increase their strength, speed, and durability to superhuman levels) though, and you've got yourself a small but very effective army.
Somewhat averted in TheAlloyOfLaw, as firearms have become commonplace, and Coinshots are possibly the only Mistings who can reliably deflect bullets (Lurchers, who have the opposite ability, generally pull bullets toward a metal plate carried on their chest).
In an episode of Lois and Clark, Lex Luthor creates a boxer that he believes can take on Superman. The boxer delivers a flurry of punches that stagger Superman. For a moment it looks like Superman is actually on the ropes, but then he simply flicks the boxer in the forehead and knocks him out.
In Star Trek: Deep Space Nine, Jem'Hadar Fighters are pretty much this. They're able to deal heavy damage, at least early on, with only a few bursts of their phased polaron beams, but a few phaser cannon shots or a single torpedo are enough to either cripple or destroy them. This is deliberate on part of the Dominion, with the Fighters being cheap but deadly throwaway ships with minimal and expendable crew, and no features that aren't essential to combat.
The Outer Limits episode "The Camp" has super strong robots that are ludicrously fragile.
The Dark Eldar are more of Glass Cannons than the Eldar, given the amount of firepower that squads of Dark Eldar can pump out for a relatively low cost and the eschewing of even what little armor their cousins use.
Harlequins are even more of a glass hammer/cannon than other Eldar. Absolutely unparalleled in hand-to-hand combat, they can rip right through a unit of Assault Terminators like tissue paper; but one good round of shooting from a basic Marine squad and they're splattered all over the landscape.
Also in tabletop, the Space Marine Thunderfire cannon. In fact, all artillery pieces were like this prior to 6th edition. As an artillery piece, anything shooting at it has a 50/50 chance of hitting either it or the Techmarine manning it. Hitting the Tech is not a huge issue, with a 2+ armor save, but if the cannon itself is hit, either a penetrating hit or glancing hit will completely destroy it (until 6th edition, when artillery guns were given a very strong Toughness value of 7 and two "wound points"). But it has a range of 60', and puts out four explosive shells per turn.
And Tau Fire Warriors, who are no tougher than Guard Stormtroopers and suck in close combat. However, they're armed with a gun that will punch through Stormtrooper armor, the Stormtrooper wearing the armor, and keep going out the back.
The Tau's Vespid allies overlap this with Fragile Speedster. They have a gun that can blast clean through Space Marine armor from 18" away, and can move reasonably quickly, but even with T4 and a 4+ armor save, they still go down like chumps to even a brief encounter with heavy bolter fire.
Ork Boyz: they have a massive amount of attacks for a rank-and-file trooper (three attacks per Boy, four on the charge), and... paper thin armor. Kinda balanced out by their ridiculously low point cost, but when they get showered by bolter fire, expect a lot of Boyz to drop.
Daemons also deserve a mention — most of them pack a punch, but die like flies against standard Imperial weaponry because their "armor" is intentionally designed to be fickle. They have a 33% chance of surviving anti-starship weapons, but a 67% chance of dying to a single small-arms round to the face.
The Imperial Guard Hellhound. Most Imperial Guard vehicles are Mighty Glacier, but the Hellhound, for all the flamethrowers it mounts, can go up with a mild hit due to the tanks being hit.
The Rogue Trader rulebook specifically describes Raider-class spacecraft as "glass cannons, able to throw out heavy fire but unable to take it in return".
Eldar and Dark Eldar spacecraft in Battlefleet Gothic have wimpy armor, no shields, ridiculously powerful engines, and some of the nastiest guns possible.
The Hunchback IIc BattleMech exemplifies this trope in the Battletech universe. It mounts two Ultra Autocannon-20s which, more or less, is apocalyptic firepower for any 'Mech (each Ultra AC can do 40 damage, which will destroy any mech its weight or less with a center hit), but sacrifices almost all of its armor in order to do so. Little wonder it's popular with Death Seeker Mechwarriors. In fact, a recent sourcebook clarifies: It was made as pretty much the Clan's equivalent of a Death sentence. Any warrior assigned to a Hunchback IIc is explicitly not expected to come back from their next battle.
In the same vein, the dinky UrbanMech mounts an AC/10, but has only 6 tons of armor—appreciable for its size of 30 tons, but still not very much. However, any light mech will be cored if Urbie hits it, and more than one Urbie makes things get very dangerous in a hurry unless you outrange them. Plus they're such cute little things!
A lot of "support" 'mechs, like the classic Catapult or the frankly ridonkulous-looking Yeoman, will mount a lot of long range weapons like LRMs, but have little armor or weapons for close-and-dirty combat.
In the novels particularly, the old Inner Sphere Rifleman 'mech is notorious as a deathtrap, with rear armor somewhere between cardboard and tin can levels. You don't want to be standing in front of it, though - each arm mounts an autocannon and medium and large lasers.
The Hellbringer (Loki) Omni is another fine example of a machine that will slaughter most enemies in its weight class and down if they get too close, but will crumple and burn if anything with a decent gun looks at it funny. Its configurations focus on massed long range hitting power, with things like particle cannons, Gauss rifles, and autocannons coming into play. The primary variant is a highly accurate killing machine with enough firepower on it to literally slag four tons of armor in a single salvo and even includes various equipment upgrades like ECM or anti missile defenses. At 65 tons and with only 8 tons of armor, though, it'll have an extremely bad day if a sufficiently armed 'Mech draws a bead on it. It's so light on armor that it actually can't even absorb an AC/20 shot dead center—something that more than a few 15-tons-lighter 'Mechs can do.
The Adder/Puma is another high grade glass cannon. Its primary configuration carries dual ER-PPC weapons and includes a targeting computer to make them highly accurate. Any 'Mech who takes a Boom, Headshot from one of those guns is down for the count, no matter the size of it. The Adder, however, is all of 35 tons, has about 6 tons of armor, and generally isn't going to stick around very long once an enemy sniffs it out.
Dungeons & Dragons 4E gives us the Striker set of classes (Ranger, Rogue, Warlock, Barbarian, though the Barbarian has pretty good HP, if lackluster starting armor): Insane damage output, but rely on the Defenders to hold down the thing they're attacking so that they don't get crushed.
3.5 psionics has the wilder class. Less than a fourth of the powers of a Psion, but can up each powers output by your level, turning a single level 3 character into something capable of cutting down much higher level enemies on average rolls. Has little health and can daze/weaken themselves afterward. Unfortunately, the downsides add up to make it Awesome, but Impractical.
Some 3.5 characters, using a number of different sourcebooks, can become this trope. As an example, take an ordinary fighter and give him Power Attack, a feat which subtracts attack accuracy in exchange for higher damage. Then take a feat called Shock Trooper, which shifts the accuracy penalty to armor class — i.e. it makes you easier to hit. This build, known as the 'Charger build' and often by the name Glass Cannon, results in a character able to do massive damage when he charges in and attacks ... but at the cost of an armor class that a small child throwing rocks could probably hit.
3.5 Rangers fit this trope: A melee-focus Ranger with Weapon Finesse(allowing the dex-focused Ranger to use dexterity for attack accuracy instead of strength, and in some cases, generally House Rule, for damage as well) and a rapier-shortsword combo can cut through quite a few opponents at or even slightly above his/her challenge rating. The trade-off is that to use the Ranger's Combat Style, which is what grants free Two Weapon Fighting feats or Ranged feats depending on choice, the Ranger can only wear light or no armor, giving him/her a low AC that most enemies can punch through with no problem.
There are plenty of Magic: The Gathering cards that have high power but low toughness. However, the card Glass Golem seems to deliberately invoke this trope.
There are various Yu-Gi-Oh! cards like: Goblin Attack Force, Indomitable Fighter Lei Lei, Spear Dragon, and Mad Archfiend that have incredibly high ATK, but zero DEF and move into defense position when it is time for your opponent to strike.
Warhammer Fantasy has a few. Night Goblin Fanatics follow it the best — they deal the same damage as a giant catapult but are even easier to kill than a normal goblin and have a chance of killing themselves. There are, however, many others.
Wood Elves are similar to 40K's Eldar, being both this and Fragile Speedsters. They have little to no armor but can give out a lot of hurt with possibly the best core units compared to their prices.
High Elves have very few units with toughness higher than 3, but they make up for it with Speed of Asuryan, gaining attack bonuses if their Initiative score is higher... and at 5 initiative on most of them, it usually is. This rule also ignores striking order penalties for weapons, so they can wield whopping weaponswilly-nilly at no penalty.
Fast Patrol Ships (formerly known as Pseudo-Fighters). They can carry devastating armament, but their shields are paper-thin. The rules even refer to them as "eggshells armed with sledgehammers." PFs with Warp Booster Packs gain extra warp-engine power, which they can pump into their weapons for an even bigger punch, but are even more vulnerable to enemy fire.
This is the modus operandi of the Norse team in Blood Bowl. Catchers/Runners get Dauntless to take down opponents far above their own weight class and Blitzers/Berserkers are Exactly What It Says on the Tin. However, every single human team member starts with an Armor Value of 7...the same as a regular goblin. This makes Attack! Attack! Attack! actually a viable strategy for them since they absolutely need to maintain the initiative. If the momentum shifts against them the entire team quickly turns into messy stains on the astrogranite...
Coinshots in Mistborn Adventure Game. Just like in the source material, these guys can essentially become human machine-guns, but they have no defensive powers and inferior Health when compared to an unpowered character.
Coffinshaker from Whats Shakin is a fairly powerful fire mage, but without his reliance of fire, is mostly vulnerable to all other attacks.
The titular Dominic Deegan shares a handful of qualities with Marvel Comics' telepaths, i.e. physically weak while mentally untouchable. He describes himself as his body being "frail and weak, but [his] mind is a fortress you have no hope of conquering."
In Sluggy Freelance, Torg is capable of killing just about anything when his Cool Sword Chaz is powered up and starts glowing. While his sword is unbreakable and nearly unstoppable, however, Torg himself is as physically vulnerable as your average human being. It doesn't help that the sword's true potential can only be unleashed when it's fueled by the blood of the innocent, a cost Torg is understandably reluctant to pay.
In Suppression, Charlie is a electricity-wielder who was kidnapped by the villains so that he could power their entire facility. He can give off enough electricity to blow off Maxwell's arm. He is also skinny as a rail and has neither armor nor the ability to take a hit.
Fairies and tiny elves in Fairy Dust are quite deadly, but can be crushed by a larger humanoid's hand in a mere swat.
Played With with the titular Kid Radd. On the offensive side, his Mega Radd is technically only able to charge enough to deal 255 damage within his own game, but thanks to sloppy programming, there's actually no preset upper limit, meaning it's as powerful as the number of bits in the console he's on. When he's out on the internet, its power is effectively limitless, making him potentially strong enough to destroy the entire internet. On the defensive side, he can only take four hits before dying, but it doesn't matter what hits him. Getting hit with a nuclear bomb does the same amount of damage as having a Mookwalk into him.
This is the case with Gralo, the Big Bad of The Night The Magic Died. While immensely powerful and capable of causing a universe wide extinction on his own, he's only protected by being able to eat any magic sent his way to a Walking Wasteland level and isn't exceptionally durable without it. Once that's bypassed, he is easily wounded and easily defeated by the Princesses.
Soundwave, of Transformers Animated, can easily take on multiple Autobots at the same time with The Power of Rock, has a massive number of various gadgets, and can control machines, but he's made of Earth machines mashed together, which means that even Sari's little hand-blast can put a hole in his shoulder, and when he is forced into melee combat, he is smashed apart in single blows. This contrasts with normal Decepticons, which are both figuratively and literally Made of Iron.
Typical firebenders in Avatar: The Last Airbender have no special defensive abilities whatsoever. The only known defensive firebending technique was invented by Iroh by studying waterbending for inspiration, and it is very situational (only useful against other firebenders). However, they are capable of laying waste on a scale the other bending disciplines are incapable of.
Eddy's Brother from Ed, Edd n Eddy. Word of God has gone on the record as saying Eddy's Brother had been dishing out pain all his life, but hadn't had it happen the other way around too often, and thus has a very low pain threshold.
In the classic Donald Duck short "Canvas Back Duck", Donald ends up in a boxing match against Pee-Wee Pete, and is only saved from a merciless pummeling when he accidentally discovers Pete has a (literal) glass jaw.
The assassin Curare from Batman Beyond seems this way. She's a deadly combatant with a sword, incredibly fast and agily, and very hard to lay a glove on, but when Batman actually manages to do so, it seems to hurt her badly.
Since the introduction of gunpowder in the High Middle Ages, Artillery Cannons are (probably) the very first and oldest definition of this trope: Deadly when given a chance to attack from a safe distance but easily neutralized by the destruction of its crew and/or the cannon itself.
Tank Destroyers. Popular back in WW2, they were Exactly What It Says on the Tin — usually armed with a tank-grade BFG to destroy enemy vehicles with great efficiency, using the mobility allowed by their lighter armor to flank enemy tanks and attack from the rear. In modern warfare, the role of tank destroyer has been taken up by helicopter gunships, though a number of lighter vehicles have been adapted to the purpose as well. American tank destroyers during World War II in particular were very lightly armored, in most cases lacking a roof for their turret which exposed the crew to all kinds of nastiness. They usually mounted a bigger gun than friendly tanks and were extremely fast: the M18 Hellcat can clock up to 55 mph on good roads.note While the same is true for early German tank destroyers ("Panzerjäger" or tank hunter), later ones ("Jagdpanzer" or hunting tanks) were built with as much or more armor as tanks, making them a Mighty Glacier, instead.
The M36 Jackson had the excellent 90mm gun which could destroy any German tank at distance. Sadly, it had a Sherman chassis and a very lightly armored body.
Another example:This. It's basically a Jeep-like vehicle with a recoilless rifle (think "bazooka") mounted on top. Or how about this: a recoilless rifle mounted on, of all things, a Vespa scooter, designed for airborne operations.
The Swedish Thirty Years' War era Leather Cannon, which could well be the Trope Namer. It was basically a copper barrel wrapped on stout leather, like cow hide. The idea was to make the cannon light enough to be mobile and easily carried, which it was. It weighed 40 kg (90 lb) and could easily be carried by two men. Unfortunately it also was prone on over-heating- leather is a good heat insulator - and tended to burst if three or more shots were shot in succession without letting the barrel cool down a bit. Purely as a weapon it was a failure, but as a concept it revolutionized the role of the field artillery.
Suicide bombers also tend to fall into this. They don't usually pack armor or a gun, but when they explode, you're in trouble.
Aircraft carriers exist to operate aircraft. Anything not related to operating aircraft, even to some extent being armed simply to defend themselves without their planes, is usually considered a waste, while the embarked aircraft give the carrier the effective ability to engage and destroy a wide variety of enemies anywhere in a radius of several hundred miles or more.
US carriers generally avert this, as they do carry a point-defense gun (that is, a specialized, automatic anti-missile multibarreled cannon with an absurd rate of fire) on port and starboard of bow and stern. This is partly US Navy doctrine to mount point-defense guns on everything (even supply ships that shouldn't ever get remotely close to any action carry them), and partly a reflection of the former USSR having developed large, long-range anti-ship missiles for the specific purpose of killing US carriers in the event of an actual war.
Almost all carriers still carry some measure of self-defense, especially against missiles. However, in 1920s, carriers were designed to carry cruiser guns, just in case they got into shooting match with surface warships (USS Lexington and Saratoga, for example, originally carried eight 8 inch guns, same as a contemporary heavy cruiser.) Post World War II Soviet carriers were heavily armed with dozens of launchers for surface-to-surface and surface-to-air missiles, to combat surface warships directly. Compared to these vessels, modern US carriers are aviation specialists.
Light tanks by definition are supposed to be very mobile, protected from small arms and constitute a serious danger. E.g. Soviet BT Tanks: on most BT-5s, 45-mm longbarrel cannon, armour 10-13 mm — price of max speed 52 km/h on tracks and 72 on wheels. Some light tanks just go over the top, however. Look at this◊ experimental monstrosity (1936-1936). It's a launcher for two fortification-busting 245-mm missiles slapped on BT-5. Max range is 1500 m. Failed to hit production run as unfit for real assault due to its crappy accuracy, slow reload and — surprise — fragility from top to bottom. Normally light tanks have nothing to do within visual range from enemy fortification even without extra explosives strapped on top.
Nuclear missiles without silos are arguably the ultimate example of glass cannons in real life, especially in the context of a nuclear war. Ballistic missile submarines have torpedoes, but they would still be in deep trouble if found. Mobile ground based units are even worse, with no defenses at all◊ against the inevitable enemy counterattacks. Of course, you're supposed to just leave before the counterattack anyway.
Conventional submarines (at least up to and including WW2 vintage) also qualify — great for crippling or killing enemy surface vessels from ambush, but they have to get fairly close to do it and again their only real defense against anything that can shoot back is not to get hit in the first place.
WWI style Monitors were shallow draft ships of questionable seaworthiness onto which the largest spare gun(s) at hand was crammed. Basically a floating artillery battery, they had the advantage of being cheap and able to get in very close to shore where traditional naval ships could not go, even going up rivers.
Anything the Finnish Navy can throw in. Their ships are crammed with oversized guns and missiles, and outfitted with minelaying equipment, but have no armor whatsoever - they rather employ hiding in the archipelago as their defensive strategy.
Humans in hunting situations. If the guns fail to bring down that bear before it closes into close quarters, prepare for a trip to the hospital. Or to funeral home.
Humans in warfare are generally a case of glass cannons in that our technological ability to inflict damage is much greater than our technological ability to defend against damage. They had to build NORAD inside a small mountain to maybe protect it against nukes.
Bob Sanders of the NFL's Indianapolis Colts. One of the league's hardest hitters, maybe the best safety in all of football... when he's healthy, which is about as rare as the Colts beating the Chargers these days. Sanders frequently spends half the regular season on the injured list, which might be because he plays so hard all the time, running full-force into offensive players on every play.
The Eagles' Michael Vick fits the archetype perfectly. With his freakish speed and arm strength, Vick is the single most dangerous playmaker in the league... as long as he doesn't get hit too hard. In 9 seasons, he's played all 16 games only once, and has spent quite a few contests limited due to one injury or another. Not counting the 2 seasons he missed while answering to "Federal Inmate #33765-183".
One recent example is Washington Nationals ace pitcher Steven Strasburg. He has overpowering stuff which can strike out a lot of batters. Unfortunately, he keeps getting injured after he makes a couple of starts on the mound.
Several examples in mixed martial arts, including fighters that have devastating offense and a weak chin.
Bob Sapp has enough strength to pick up a 260 pound man literally off the mat and piledrive◊ him violently to the ground. Yes, in MMA, where piledrivers are neither safe nor done with compliance from the victim. He beat one of the best kickboxers in the world (Ernesto Hoost) twice in 2002. Sapp is also known for the trifecta of having a glass chin, possessing very little toughness or heart, and having laughably few grappling skills. He lost in 2009 to a man 150 pounds lighter than him who fancies himself a superhero, sports a mullet, and goes by the name "Minowaman."
Melvin Manhoef, a dutch kickboxer, has truly horrifying punching power. He was the first, and so far only man to ever knock out Mark Hunt, who was famous for shrugging off career-ending strikes to his presumably granite-filled head. Manhoef delivered said KO◊ while moving backwards. Unfortunately, even though he's fought at the highest levels of kickboxing and MMA and can put together beautiful offensive combinations, Manhoef's strike defense is quite lacking, and he has been knocked out by mid-level fighters far more often than an elite striker should. More saliently, his grappling skills are pure garbage. For MMA professionals, fighting Manhoef can either end in Melvin decapitating you with a punch, or with him meekly tapping out 15 seconds after the fight hits the mat.
Many fighters like Melvin Guillard and Houston Alexander have decent striking, scary power and zero grappling skill. Stand with them and they're likely to hurt you, take them down and they'll play you the three-tap symphony.
Julian Jackson was a boxer whose career spanned the 80s and the early to mid 90s, and is boxing's patron saint of the one punch knockout. Being in the ring with Jackson was to always potentially be one punch away from being KO'd. However, some of Jackson's victims were only knocked out because they knew of the weakness in Jackson's chin and tried to knock him out first. The most prominent example is probably Herol Graham, a slick defensive specialist who made his living by dodging punches and countering his way to a decision. Graham was able to hurt Jackson consistently in the first three rounds of their fight, so he pushed the action and had Jackson backing up in the 4th. Then Jackson connected with a single blow and not only was Graham unconscious before he hit the canvas, he remained out for minutes afterward. Final round and aftermath of the Jackson-Graham fight. When attempting to move up a weight, Jackson was smashed up twice by Gerald Mc Clellan, whose career was subsequently ended by another fighter with Glass Cannon tendencies: Nigel Benn was also a boxer with an almighty punch but a suspect chin, who was knocked down twice during the fight but got up and finished by putting Mc Clellan in hospital.
Some would say that British heavyweight Frank Bruno was also a Glass Cannon. A punch that could stop almost anything if landed properly, but a bit slow and unwieldy, and against top opposition, liable to be vulnerable to a big hit, not because he would get knocked down - which might have given him some time to recover - but because he would stay on his feet while stunned enough for the subsequent series of punches to finish the fight.
Late in Mike Tyson's career Tyson's old trainer Kevin Rooney who coached him in his prime complained that Tyson was no longer the elusive Lightning Bruiser who had once dominated the boxing world. "His style was to use head movement, be elusive. He's not using the style the way he's supposed to be. He's just... he's just a puncher now. If he hits you, he'll knock you out. If you hit him, you'll knock him out".
Manny Pacquiao became a superstar boxer because of his freakish speed and strength which he used to overwhelm his opponents into submission, despite his small size. However, Manny Pacquiao also has a very fragile chin that can get damage when timed right. Earlier in his career, Pacquiao could easily get knocked down and out. However, after mastering his offense under the training of Freddie Roach (a well known offensive trainer), Pacquiao went a decade destroying some of the top boxers of his generation. That is until his nemesis Juan Manuel Marquez who he could never get a clear victory over, once again exposed his weakness by brutally knocking him out in their 4th fight by a well timed counter hook.
Roger Mayweather, long time trainer of Floyd Mayweather Jr. had all the offensive skills of his nephew and was a two-time world champion. However, unlike Floyd Mayweather Jr., Roger Mayweather didn't have the great defense or strong chin. In fact, Roger's chin was so fragile that even the slightest force against it could cause him to get knocked out. This resulted in many upset losses against opponents he should've easily beaten on paper. The biggest example is against Rocky Lockridge.
Mosquitoes. Their bite can transmit nasty diseases like Malaria, Dengue, Encephalitis and Heartworm, enough to kill or cripple a human for days. On the bright side, a well-timed smack kills them instantly (usually).
Hockey player Eric Lindros was widely heralded as "The Next One" by pro scouts in the late 1980s and early 1990s in reference to Wayne Gretzky, who was in turn called "The Great One" for being the all-time best player to ever put on skates. Lindros was the size of a train and dealt out hits to match, and was a highly skilled scorer to boot. When he made it to the NHL, he was both one of the most dominant and the most injured players in the league.
The Argentina national team was accused of this during the 2010 World Cup. Their dynamic and amazing offense blew teams away, until the Germans, who were able to shut down Argentina's scoring attempts, carved its way through the Argentines' notoriously weak defense in an absolutely brutal match.
David Luiz, the most expensive defender in football/soccer. The Brazilian can deliver attacking free kicks without breaking a sweat- and he's a centre-back. As for defensive ability... it came to a head in the 2014 FIFA World Cup in Brazil, when he captained his side on a fateful day in Belo Horizonte. 
More or less the situation with human-held firearms these days. Armor is bulky and unwieldy and guns and ammunition that can penetrate said armor are readily available, even for common criminals, so often it comes down to trying to make sure that you can shoot first and that your opponent can't shoot back.
Cars. Arguably better at killing people and destroying things than guns, but quickly fall apart if they hit things. Granted the things they're good at destroying and the things that destroy them if hit aren't one and the same, but since you're from Column A, it's still a good idea to look up from your smartphone before you cross the street.
Older cars were sturdier. Modern cars damage easily in an impact because it's realised that what matters is not whether the car is damaged but whether the *occupants* are, so crumple zones are better than a really rigid shell.
Birds of prey. They have sharp and strong beaks and talons, capable of killing their prey in a split second... but if grounded by a broken wing or leg they are very likely to die of starvation.
Venomous snakes also. Sure, they have a very nasty weapon at their disposal, but the instant their venom glands run dry they're reduced to bluff or flight. And if an attacker is too thick-skinned or immune, they're lunch.
Combat Robotics has a surprising number of glass cannons. In Robot Wars, Razer had an almost unstoppable weapon, but often broke down of its own accord. Tsunami and Wheely Big Cheese had immensely powerful flippers (but the latter was very difficult to aim) but lacked the durability to fight Lightning Bruisers like Chaos 2 and Mighty Glaciers like Xterminator. In BattleBots, Nightmare had a massive 4 foot diameter spinning disc, and its destructive power was the original reason for the arena having a ceiling, but its wheels were very vulnerable. It lost after having a wheel (and sometimes the gearbox and part of the motor it was attached to) ripped off by horizontal spinners. Many "shell spinners" have huge destructive power, but if they get flipped over, they're toast. Finally, Last Rites, one of the current top-ranked heavyweights, practically defines this trope. Even the most heavily armored opponents cannot simply shrug off blows from its spinning bar, but it is lightly armored, and its wheels are vulnerable to a solid hit to the side. In fact, because its bar is so powerful, and so much weight is poured into the weapon system, it is frequently defeated by the recoil from its own attacks.
The Prussian infantrymen of Frederick The Great were renowned for their rapid rate of fire (pretty impressive, given the rather slow firing rate of muzzle-loaded muskets) but were pretty vulnerable in close combat, making them a ripe target for cavalry. Fortunately, Frederick was enough of a tactical genius and a lucky man to prevent decisive defeats.
Irukandji jellyfish. They are the size of a fingernail and are so fragile they can't be kept in a tank - they will die from bumping into the glass. They also have a venom that, while it is not lethal, will hurt you so very much that you will wish it was.
The Mitsubishi A6M Zero was extremely fragile, with no armor and fuel tanks that would leak continuously from even the smallest puncture instead of sealing like Allied tanks, so that even the most minor glancing hit could destroy it. It also had better armament than any of its rivals and could blast apart most Allied aircraft with a single burst, and a turn rate good enough to get into a firing position against even the most elusive enemy. It was the king of the Pacific skies until faster American fighters showed up that could simply barrel down on a Zero from above, destroy it, and run away before the Zero's wingmates could respond.
ME-163 Komet. It was a rocket fighter armed with two 30mm cannon or ten short ranged upward-firing single-use guns. It was designed to kill bombers with just a couple of hits and during its powered flight phase, moved too quickly to be targeted by the prop driven Allied planes. However, it only had enough fuel for about 7 minutes of powered flight and once it expended its fuel, it was a nearly helpless glider.
The Soviet Union produced an example. The 2B1 Oka was the largest self-propelled artillery piece ever built, and could fire a 420mm nuclear projectile from it's 65-foot-long barrel up to 28 miles downrange. Unfortunately, the recoil of such a monster cannon was too powerful, damaging the gun mount, snapping the treads, and tearing up the transmission. Assuming it even could fire a second shot, it would be effectively a stationary artillery piece.
Traditionally, archers in many armies did not wear any armor, partly because it would have interfered with their movements and also because they generally could not afford it. A particularly well-off bowman might be able to go into battle with a sword and buckler, a breastplate, and a helmet of some sort; most went off to fight with little more than a knife and the clothes on their back (and sometimes even less than that). Suffice to say, archers tended to get slaughtered if the fight came to them.
In a way, elephants are this; they're extremely powerful, and fairly fast as well. Yet due to Square/Cube Law, tripping can greatly injure them.
War Elephants are not much better. Sure, they seem like they would be a Mighty Glacier at the very least, able to suck up lots of arrows and trample enemies, but they scare VERY easily, uncontrollably running away, often through friendly lines.
Modern Guided Missile Warships certainly count. The CG-47 "Ticonderoga" class cruisers started life as destroyers, but with some design changes (and some meddling from DC) they became cruisers. To give you an idea of what this means, think of it this way. Each 'Tico' is armed with two 5" rapid fire cannons for short range work, as well as Harpoons and Tomahawks for long range work. Both of those missiles are capable of ripping other ships apart from many, many miles away, and the 5" guns can track anything from small boats to low flying aircraft, and reliably take them down. But the armor is made of KEVLAR. Yes, the EXACT same material that soldiers put on to protect them from bullets. This was done to save weight since the hull was never designed for cruiser specs. Those aboard a Tico better hope that the AEGIS combat system doesn't Blue Screen... Not that armor would be of any value against modern anti-ship missiles however, especially as the primary means of damage is fire not the explosion itself.
Also of note is the "Kirov" Class of Battlecruisers. Each ship is armed with a an array of the appropriately named "Shipwreck" Anti-ship Missile, but the armor is only 76mm thick. There's been an ongoing debate over what would win, an Iowa or a Kirov. However, since the Iowas would likely be protected by the aforementioned Ticonderogas, and their GC Brothers the Arliegh Burkes, the Kirov would have to rely on a Macross Missile Massacre to hopefully destroy the battlegroup. If it fails to do so... In this case it would be the destroyers that would be doing most of the defensive work, the armor and big guns of the battleship would be almost entirely irrelevant in terms of winning such a battle, although the Tomahawk and Harpoon missile launchers which were fitted to the battleships in the 80's would give them an ability to shoot back.
Most modern warships fall under this design philosophy. Modern anti-ship weapons have such long range and sheer destructive power that it is simply impractical to carry enough armor protection to be useful, except for certain key areas such as the ship's ammo magazine.. Instead, the extra weight is either removed from the equation to allow the ships to move faster, or used on more useful things, such as the aforementioned long-range highly destructive missiles. In short, modern shipbuilders take to heart the saying that the best defense is a good offense.
World War II era Japanese Mogami class cruisers. Intended to conform to the requirements of the London Naval Treaty while maximizing armaments, the ships were designed for 9000 ton displacement while packing 'fifteen' 6-inch guns and a dozen 24 inch torpedo tubes. Unfortunately, the construction techniques that the Japanese were using did not quite pan out. The ships became notorious for their instability and structural weakness (the ship's armor plates buckled and split when the guns were being test fired!), requiring massive refit to make them serviceable. In the end, they weighed in nearly 4000 tons heavier than original design and somewhat unfairly came to be used as poster boy for how the Japanese grossly violated arms limitation treaties.