A children's picture book actually has this as a plot point. A child is playing outside this apartment complex, and loses a toy to the other side of the road (either a plane or a ball). Since he had been forbidden to cross the street by himself, he tries to ask passing adults to escort him across the street but nobody does anything. Finally, he decides to climb up some objects such as a tree, then his weight causes the top of the tree to lean, allowing him to grab the tree on the other side of the road, where he picked up his toy and threw it back across the street, and repeated the process to get back across. His reasoning for doing this was because he didn't actually set foot on the street, and he was forbidden from walking across the street without an escort - his mother had not told him he couldn't find another creative way across. A unique example in that it leaves the spirit of the rule intact: presumably it's meant to keep him safe from oncoming traffic, and by bypassing the street, he avoided that danger. Though the potential danger of climbing trees is another story.
According to Captain Bartleby in 1636: The Saxon Uprising, there's no rule that the Dollar is the exclusive currency of the USE, allowing the Third Division the capability to produce its own currency for purchasing supplies.
In The Acts of Caine, a human surgically altered to look like an elf meets the exiled elf prince, who has been trapped in a human brothel for centuries and just wants to go home. The human, with his rather obsessive knowledge of elven court customs, finds a way to get around the exile: If the human meets with the elven king and presents the exiled prince as a gift, the king will be forced to take his son back and treat him well. When they try this trick however, they find out that the elf king had long since rescinded the exile, having deeply regretted sending his son away, and welcomed him back with open arms. What's more, the human was adopted into the royal family for bringing the prince back.
In The Adventures of Captain Vrungel, the captain finds himself in trouble because his ship is carrying a load of squirrels rescued from a burning forest. Naturally, the customs demands he pay a tariff. So, the captain takes two paddle wheels, connects them to a giant hamster wheel, puts the squirrels inside, and states that according to the law, you don't pay tariffs for elements of the ship's propulsion system.
Similarly, joining in an escape attempt after giving your parole is forbidden, but being rescued is allowed. Imprisoned by Hanover after the mutiny on HMS Hermione, Alexis refuses to give parole, then plans and executes a breakout after the Berry March fleet is recalled to guard the Hanoverese interior with the expectation that their next jailors won't be as accommodating, even stopping to pick up her Ungrateful Bastard captain and the other officers and midshipmen.
The Accords also ban Orbital Bombardment on pain of death, but Alexis, desperate to buy time for badly outnumbered ground troops, discovers on a close reading that "space" is defined in the Accords as "above a planet's mesosphere". She has her barque's hull stripped of masts and sails to fly through the lower atmosphere and begins blowing holes in the Hanoverese columns.
The brutal and horribly sexist Captain Neals, as much as he hates the very idea of Alexis being in the Navy, cannot legally have her flogged. Then she disobeys his demand to beg forgiveness on bended knee, stating that she will bow only to her Queen, and he disrates her (busting her down to crew), and promptly gives her two dozen lashes on general principles. This sparks a mutiny.
Amelia Peabody: During her son's childhood, Amelia is always forbidding Ramses from speaking of something or carrying out some action or another, and then adding extra details to her prohibitions while mentally noting that he's already thinking of ways to get around it and that she needs to be careful to close these loopholes before he can make use of them. For instance, forbidding him from leaving his room unless there is genuine danger that will result if he stays in it (as seen in Deeds of the Disturber, when he's been ordered to stay in his room, but leaves in order to alert his mother that said room is on fire).
In Animorphs, to prevent the destruction of the galaxy that will be inevitable should they come to direct blows, the Ellimist and the Crayak set a bunch of rules for themselves in how to resolve their conflict... and then find as many loopholes as they possibly can. The Ellimist isn't allowed to directly save all humans from the Yeerks, but can take a small sampling of them and relocate them on another planet? Show the world's anti-Yeerk heroes a possible future to encourage them to agree to relocation... but give them a massive hint for how they can score a decisive victory over the Yeerks in the process. The Crayak's lackey, the Drode, isn't allowed to kill any sentient life? Set the self-destruct sequence on a bunch of robots (robots aren't alive!) to draw his targets into a situation likely (but not guaranteed) to kill them.
Holly Short's final test at the police academy was an Unwinnable Training Simulation where she was facing an insurmountable number of virtual enemies. She fired at the projector instead.
In the first book, Holly Short interprets a cry for help from someone who has no idea she's there as an "invitation" enabling her to enter a human building. She has to argue over this to her commander later, when she states that there is actually precedent for it. Of course it's later shown that Fairies who enter homes without invitations become violently ill as a result, so her ability to enter without getting sick should speak for itself.
In the first book, Artemis makes the mistake of saying that no fairy may enter his house while he's alive. The fairies notice this, of course, and decide to just kill him. And that's exactly what he wanted.
In the third book, when joking (and unsuspecting) permission for Juliet to bring her "invisible friend" is also used as an invitation.
When Artemis allows himself to be captured, Spiro gives him a tour of the building's security system to show him just how screwed he is. Artemis jokingly says he could beat the security with the help of his fairy friends. Spiro tells him he can bring in all the fairy friends he wants. Oops.
In the prequel story, LEPrecon, which shows how Holly got into the LEP. Her test is interupted by Turnball Root, and it ends up at a point where Commander Root and Trouble Kelp are locked inside a human dwelling. Holly can't go in to save them, so she gets the ship and tears the house down. You can't get dwelling sickness if there's no dwelling!
The Robot stories are a study in Loophole Abuse. Robots must obey the Three Laws, but many of the stories place a Robot in a situation where strict adherence to the Three Laws is impossible, and so the Robot must engage in some judicious moral wrangling to reach a resolution. Sometimes it boils down to a "spirit of the law" versus "letter of the law" situation. Other times it involves situational interpretation of the Laws (i.e., a Robot cannot harm a human, but what constitutes "harm?" Does social embarrassment count as "harm?" etc.) Chronologically later stories involve the creation of a "Zeroth Law," and introduces the concept of the "Greater Good" into the Robots' morality.
"Little Lost Robot": Susan Calvin gets called to find a missing robot in a space base, because it had been told to "get lost", and it joined a recently come group of physically identical robots. Susan tried to weed the lost robot out by simulating a human getting crushed under a weight, because she knew the First Law ("A robot may not injure a human being or, through inaction, allow a human being to come to harm") had not been fully implemented (becoming "A robot may not injure a human being"), but they all jumped. The next experiment she conducted, a similar test but placing something between the robots and the human that would have killed them, none of the robots moved. When she asked the robots about the incident, they stated that one of them had convinced the others that uselessly sacrificing their lives for one human would mean none of them would be around to protect any humans later.
Robots and Empire: The Three Laws must be maintained (by that point; early in the development of robotics they could be altered), but it is entirely possible to restrict the definition of human so that most outsiders would be excluded from it...
Dr Lanning tries to raise the point that a robot couldn't be a criminal prosecutor, because success would result in harm to a human, violating the First Law. However, Dr Calvin explains a nuance of the First Law (a precursor to Zeroth Law Rebellion), where his actions are designed to prevent harm to a majority of humans. He's also not causing harm directly, only presenting facts to another human, who makes the decision, and recommending the elimination of the death penalty.
Stephen Byerley is accused of being a robot during a political campaign. Byerley avoids any attempt at examining him to outright confirm the allegation, and secondary proofs (he can eat) are easily explained as part of the disguise. Finally, a man accosts him during a speech and demands that Byerley punch him, to which Byerley reluctantly complies, thus violating the First Law. Dr Calvin confirms that this proves him to be human. However, in private, Calvin admits that Byerley could have faked this proof, too; robots can't hurt humans, but they can hurt other robots that look like humans.
Bearskin: Part of the Deal with the Devil is that the soldier isn't permitted to pray for help. He gets around this by giving generously to the poor and asking them to pray for him, instead, and it works: he survives, keeps the unlimited supply of gold, and gets the girl. If only the story ended there...
In a The Berenstain Bears novel, the new principal puts in a school dress code. They proceed to piss him off on the very first day it's in effect by doing just this. Among these are wearing green jeans instead of blue jeans, and wearing a Batman cape instead of a Superman cape.
In Bimbos of the Death Sun, a sci-fi convention holds a writing contest. The winning entrant turns out to be an English teacher; when her daughter goes up on stage to accept the award, she remarks that the rules said the contest was open to all, regardless of skill level or professional talent. Marion Farley, the college literature professor who judged the contest, responds by muttering "Figures..." under her breath.
In the apocryphal Book of Judith, when she was asked by Holofernes to give a "trustworthy report" concerning the Judean forces that were holed up on the mountain in Bethulia, Judith responds, "I will say nothing false to my lord." Although Holofernes did not know that Judith had actually meant The Lord in her response to him.
Callahan's Crosstime Saloon: Callahan's Bar has a very strict rule against asking prying questions of someone who doesn't want to talk, enforced by the piano player's blackjack.
As a card-carrying Sophist, I will now proceed to make some prying statements, and if you choose to react to any of them it won't be my place to stop you.
In Castle Hangnail, Molly must satisfy a list of conditions in order to be recognised as a Wicked Witch and the Mistress of Castle Hangnail, including defending the castle from invasion and winning the loyalty of the nearby villagers. She ends up satisfying most of the conditions in ways that technically fit the requirements but might not be considered within the spirit, such as winning over the villagers by being a Karmic Trickster rather than by terrorizing them into submission. She also initially tackles the "defend the castle from invasion" condition by routing the weeds that have invaded the castle's neglected gardens, but she does end up filling that one properly after an evil sorceress tries to take the castle for herself.
Chrestomanci: In The Lives of Christopher Chant, in order to rescue his friend Tacroy, Christopher has to find Tacroy's soul and claim it from the Priest-King (the Dright) who rules Tacroy's home dimension and owns everyone in it. When Christopher does see the soul, it immediately becomes much farther away from him. When Christopher claims the Sept is cheating, he casually points out that "I named no rules." At which point Christopher and Millie follow suit, because if there's no rule to say the Sept can't use magic to interfere, then there's no rule to say they can't use their magic to stop him interfering.
Immediately after this, the Dright asks for one of Christopher's lives in return for Tacroy's soul, but Christopher realizes that this will grant the Dright control over him. Chistopher thus gives the Dright one of his lives and immediately sets it on fire. (It did hurt a bit.)
The Pevensies justify wearing fur coats that don't belong to them on their foray into another, wintery world, on the grounds that they won't even be taking them out of the wardrobe.
King Aslan pulls this off in a plan against the White Witch. According to the rules of the Deep Magic, Edmund must be killed on the Stone Table because he was a traitor. Aslan then offers to go in his stead and die. Turns out he was banking on the rules of the Deeper Magic, a rule that Jadis didn't know of, to bail him out: if someone who is innocent is sacrificed on the Stone Table, then that person is revived. Guess who Aslan is.
In John C. Wright's Count To A Trillion, Menelaus tries a nutty, very hypothetical, and dangerous experiment as soon as the shuttle leaves Earth — meaning he's no longer covered by Earth law, and not yet under the captain's authority on the ship. Reaction to this reasoning: they knew they shouldn't have brought along a lawyer.
In the short story "Nothing in the Rules", one team at a girls' swimming competition contains a mermaid, who wins everything. In response to the opposition's outrage, the team coach points out that the rules only specify that all entrants must be female; nothing is said about species. The officials are reluctantly forced to admit that he's right. Whereupon the opposing coach visits the city zoo and borrows a female seal, who (properly incentivized with a bucket of fish) outswims the mermaid. To avoid disqualification for not using the proper swimming form, the mermaid only competes in the freestyle events.
In Throwback a genetically recreated prehistoric human becomes a football player. In this case any "humans only" rules don't apply because before the story began the recreated cavemen fought for their civil rights and were legally recognized as people, even though they are technically not the same species as most humans.
The Diabolic: Nemesis values Sidonia's life above all other things, above Sidonia's desires and especially her own life. Sidonia, who just wants Nemesis to live, finds a way to make her prioritize her own life: She tells her that if Nemesis dies, she'll kill herself. With no other option, Nemesis agrees.
Nemesis: All right. All right. I'll come back alive. I will do everything in my power to preserve my own life as I would preserve yours. I'll do it or I'll destroy this Empire trying.
In one of the Dinotopia books (Lost City), the newcomers to the lost Troodon warrior haven of Halcyon are challenged to complete either an underground maze or an obstacle course against one of the residents. The rules of the obstacle course are, simply, to get from one end to the other before the opponent completes his own course... but the honor-bound saurians had never previously considered the strategy of avoiding all of the obstacles and running down the empty ground between the two courses...
In the same book, two high-ranking officials play an oral wargame, declaring what they order their troops and what not. It eventually gets down to the generals preparing to go one on one on a bridge. Then the villain claims the Kraken rises up from the water and grabs his opponent. In retaliation his opponent declares that the Kraken isn't a bloodthirsty monster, but just wants a friend. The Judges declare it legal, and the villain loses.
In Wyrd Sisters, it's mentioned that witches and warlocks aren't supposed to leave their homes on Hogswatchnight (the Discworld equivalent of Christmas/New Year's). Granny Weatherwax just ignores this rule like she does so many others, but Nanny Ogg gets around it by inviting the entire town to her house for a party. It helps that she's related to most of them.
One Auditor who has assumed a human body finds she can overcome the compulsion to obey rules by declaring that certain things are "bloody stupid"; "bloody stupid" things can be safely ignored. This was written into the rules because regular auditors were paralyzed with indecision if confronted with a paradoxical statement, like a sign saying "Ignore this sign", or a sign next to an empty cage that says "do not feed the elephant".
The horsepersons of the Apocalypse must ride out at the end of the world. No-one ever said against whom.
Susan's thought process in Soul Music, on the subject of leaving school without permission:
Susan: There's going to be trouble over this. ... I'm on the back of a horse a hundred feet up in the air, being taken somewhere mysterious that's a bit like a magic land with goblins and talking animals. There's only so much more trouble I could get into... Besides, is riding a flying horse against school rules? I bet it's not written down anywhere.
Likewise with Gnome Watch officer Buggy Swires; in a companion book, he is said to have a natural resistance to rules and authority. Even the unwritten rules like "Do not attempt to eat this Giraffe" or "don't kick people in the head because they won't give you a chip".
In Discworld, the laws of nature work like this; Ponder Stibbons has discovered that, like a busy local authority, the universe has failed to forbid a lot of things simply because it never occurred to it anyone would do them. The trick is to get things done before the universe rewrites the rulebook and pretends it was impossible all along. The breakthrough came with the invention of Hex, which can repeat the same spell several times a minute in minutely different ways, the universe making each one impossible just too late, allowing him to (for example) assemble the texts of books that haven't yet been written.
The climax of Unseen Academicals hinges on a long-forgotten, sometimes-derided football rule specifying that the first object handled by three consecutive players in a game shall be considered the ball. This allows the young hero to put his tin-can-kicking skills to brilliant use when the original game ball is "lost". (Since he has more skill kicking a tin can versus a "legitimate" ball, they need the rule to get that skill into play.)
Bledlow Nobbs:[no relation] Are we going to cheat? Nutt: No. We are going to stick to the rules. And the thing about sticking to the rules is that it's sometimes better than cheating.
In the City Watch books there's a few loopholes in the traditional watchmen's oath, which requires new recruits to swear to "uphold the Laws and Ordinances of the city of Ankh-Morpork, serve the public trust, and defend the subjects of His/Her Majesty". As many fans have noticed, there's nothing in there about defending the ruler (just his/her subjects), and in Night Watch Discworld Vimes points out it doesn't say anything about following orders.
In Jingo, when Ankh-Morpork declares war on Klatch, Lord Rust takes over the city, declares martial law and dissolves the Watch. However, since Vimes is a knight and therefore a nobleman, he is able to revive the Watch by declaring it his private army, which, by law, every nobleman is required to provide for the war effort. When Rust tries to assert command over "Sir Samuel Vimes' First of Foot", Vimes points out that, under the law, he only has to answer to "the king or his duly appointed representative", there having been no king since Vimes' own ancestor beheaded the last one over two hundred years ago. Rust could technically force the issue under the same technicality that allows him to take power anyway, but it's an open secret that the rightful heir to the throne is Vimes' second in command.
This trope is how the Librarian is able to keep his job at Unseen University, despite his transformation; There's no rule barring an orangutan from the college council, though the wizards had looked very hard for one. This also enables him to read the Necrotelecomnicon without harm; it contains things manwas not meant to know, nobody said anything about apes.
Albert: You're not allowed to do that... Death: THE HOGFATHER CAN. THE HOGFATHER GIVES PRESENTS. THERE'S NO BETTER PRESENT THAN A FUTURE.
A minor example in Going Postal, where the Grand Trunk clacks (similar to telegram) company and the Post Office agree to a race to get a message to a distant location. As a respected figure, Arch-Chancellor Ridcully is selected to decide the message, and not liking the clacks company very much he chooses a magical textbook, pointing out that no one said it had to be a letter. So while the Post Office can throw a book on the mail cart as easily as an envelope, it takes the clacks hours to translate the text, pictures and diagrams into a form they can easily send. Moist then shows up to the race with a broomstick, and when called on it points out the Trunk could do a similar exploit with a "pony express" relay (or more to the point use horses to get around technical issues in a single tower); after both agree to the rules change Ridcully cheerfully points out that painting stars on a normal broom doesn't make it magic.
As described on Pet Heir, Topsy Lavish uses this in Making Money to prevent having to leave ownership of the bank to her greedy relatives. If she directly bequeathed ownership outside the family, her relatives would challenge the will. So she bequeaths 51% of the shares to her dog, and then bequeaths the dog to the protagonist.
In The Dresden Files, there are lots of different sets of rules that must be followed. As expected, many of the characters spend a lot of time finding loopholes in them:
In Dead Beat, he gets away with necromancy because technicallythe Fifth Law of Magic only applies to human dead, not animals like Tyrannosaurs. It probably helped that it was both necessary to saving the world and downright awe-inspiring.
The Sidhe (the "fairy lords") are physically incapable of lying or breaking their word, but they are basically made of loophole abuse. Some notable examples include:
Harry's crazy godmother Lea swears to give Harry a temporary break from trying to take him captive so he can go save the world. She explicitly does not swear not to send one of her minions to do it for her.
Part of Harry's deal with Mab, to perform three services for her, is an agreement that she won't use her powers against him for refusing to accept. She promptly uses her powers to put Harry in a lot of pain — but not to extort his cooperation, but just because she likes doing so.
While being hunted by the gruffs, Harry considers cashing in his boon from Summer to protect him. He reconsiders when he realizes that they could "protect" him by severely injuring him badly enough to take him off-mission so the gruffs no longer considered him a threat.
When Harry meets the Eldest Gruff, who actually likes Harry but is Just Following Orders. Gruff is still required to try to kill him as long as they are both on the field of battle, and being a Fairy he physically cannot ignore this order. Of course Harry has a boon with the Summer Court, which Eldest Gruff ALSO can't ignore. So he asks for a doughnut. And not a magicked doughnut, but a fresh one. With sprinkles.. This forces Gruff to leave for long enough for Harry to get away as well.
At Harry's birthday party in Cold Days, one of Mab's rules is that no blood may be spilled. It turns out there are plenty of ways to kill someone without spilling blood, all of them perfectly acceptable.
In Proven Guilty, five of the seven Senior Council members are absent at Molly's trial, the Merlin holding their votes as well as his own. He casts them all to execute Molly immediately, but Harry insists that all votes need to be cast before the verdict is passed, even though the only remaining juror, the Gatekeeper, can't change the outcome. The Gatekeeper then insists he needs time to consider, and delays until the three absentees who Harry counted on to support him arrive. Since the vote isn't officially over, the Merlin's votes on their behalf are invalidated and Molly is allowed to become Harry's apprentice.
When he accidentally lands in the Erlking's domain, the goblin sarcastically refers to Harry as his "guest" so Harry seizes upon that, claiming the protections of guest right. (It gets pointed out that the Erlking could use his own loophole: keeping any guests in his domain as long as he wants [as long as they aren't harmed, but that's a general rule]; Harry's quest is a bit time sensitive, and would fail if he doesn't leave soon.)
In Ghost Story, he's told only crazy ghosts can become corporeal and interact with the real world, and quickly realizes that the actions he takes, the things he does, marks him as more than slightly unhinged. Welcome to the real world, ghost Harry!
On the other hand, he also knows when he's outmatched in the loophole-fu department: when he agrees to become Mab's Winter Knight he doesn't even try to weasel his way out of it using Sidhe logic, because he knows he'd fail. Instead he hires Kincaid to kill him the next morning, then has Molly erase his memory of doing so.
In Skin Game, Michael (a crippled and retired Knight of the Cross) promises Nicodemus (a very dangerous host to a very dangerous Fallen Angel) that he will step outside his house's protective barrier in exchange for his friends' safety. Michael is a good enough man that the Archangel Uriel himself comes down to try and get him to stop. Unfortunately, angels can't interfere with free will, so he can't actually prevent him from leaving. And due to the Balance Between Good and Evil, Uriel can't heal Michael, since that would give an opportunity for an equally powerful demon to act as well. Uriel then chooses to exercise his own free will by loaning Michael his Grace, his angelic power, essentially turning him into an archangel for a moment—with the happy side effect of curing all his wounds for as long as the power is within him. Since Uriel can destroy galaxies with a thought, Harry compares this to loaning someone a jumbo jet because he needed a reading light. Uriel agrees, but points out that Michael really needed that reading light. And if Michael does anything he shouldn't with the power, Uriel will Fall, and they'll have a second Lucifer on their hands. On a related note, Michael promised Nicodemus he'd step outside his house's protective barrier. He never promised to surrender.
Dune: can be applied to using outlawed weapons, but is a legal gray/grey area.
In the Dune universe, there is a major prohibition against using nuclear weapons against human targets. Just before the final battle, Muad'Dib uses a nuke to blow a hole in a large rock formation so his army can pass through. He points out that no humans were killed by the nuke. It is pointed out that this is sophistry, but Muad'Dib counters that the Guild, whose ships are orbiting the planet, will take any excuse to not be obligated by the Great Convention to destroy Arrakis.
The Eldraeverse nanofic "But I Don't Need One For This!" comprises a very long list of vehicles which some Expansion Regions government added to those requiring licenses to operate, following a series of incidents with tourists from the highly libertist Empire.
Due to being forced to obey any order to the letter, Ella from Ella Enchanted is good at this. Sometimes she does it simply because she can. For example, at her mother's funeral, her father orders her to change her dress. She intentionally picks one that's inappropriate for the situation because it was one of her mother's favorites, though she really gains nothing from it.
Empire from the Ashes reveals a cruel and very long-running example in the second novel. As it turns out, the reason for the Achuultani's period deathsweeps is solely to ensure that they operate in a permanent state of emergency — they are ruled by an AI which came into power under emergency protocols, unshackling it from limitations and investing it with authority to face the crisis... which then promptly realized that nothing stopped it from having its 'solutions' lead to a new crisis that would allow it to remain in power forever.
Ender's Game. Ender is faced with a horribly unbalanced game against two teams at once. Ender wins due to the victory condition just being opening the enemy's gate, without bothering to actually fight the enemy soldiers.
This was very deliberately done, a big deal is later made about war having no rules, and anything you can do to win is what you should do. (Apparently a war to extinction against aliens has no Geneva Convention). Later, while he's playing a simulation in which he was leading a campaign against the Buggers, the final confrontation gave him only a few, old ships against the Buggers' home planet surrounded by warships. He blows up the planet. And then it wasn't a simulation after all...
Early in Escape from the Isle of the Lost: a Descendants Novel, the Seniors at Aurodon Prep are participating in an annual scavenger hunt. One of the items on the list is to kiss a prince, so three of the girls give Ben a kiss on the cheek to complete that part of the challenge. However, they lose, because Ben has already been crowned king, and therefore doesn't count. Meanwhile, Chad Charming, a prince himself, snags victory by kissing the back of his own hand.
The alien frogs in Tom Holt's Falling Sideways have a very clear rule about Thou Shalt Not Kill. They do not have a very clear rule about Thou Shalt Not Make People Believe Themselves To Be Frogs And Therefore Starve To Death On An Unsuitable Diet.
In The False Mirror, Ranji-aar's team was going through a large maze and discovered that the other team had bribed people, and had learned the route. So they made a ladder to get up on top of the walls, away from all the obstacles, and fake environmental dangers. Needless to say they won.
In Fate/Zero, Kiritsugu signs a Magically Binding Contract with Lord El-Melloi - El-Melloi will order Lancer to commit suicide and withdraw from the Holy Grail War, and in exchange Kiritsugu cannot harm him or his fiance Sola-Ui (whom Kiritsugu is holding hostage). As soon as Lancer is dead, Kiritsugu's partner Maiya guns down both Sola-Ui and El-Melloi.
This is highly ironic, because Lord El-Melloi did use this trope as well. He had already modified and exploited the contract system so that, while he carried the Command Seals, Sola-Ui was the one supplying Lancer with the prana he needed. This allowed El-Melloi to fight at full strength without needing to worry about sharing his prana between himself and his Servant.
Kiritsugu again: Ain't No Rule that the Einzbern Master has to be an Einzbern, or that a Master has to be the one who supports his Servant.
The Black Knight's swordplay is so practiced that he can perform even his most advanced techniques instinctually, represented by the "Eternal Arms Mastership" ability. This allows him to ignore the mental restrictions of his Berserker class completely, while keeping the improved stats.
Five Kingdoms: In Death Weavers, when Cole travels to see Dandalus, Warden of the Light, he is told that he may ask three questions of him. Cole has some important questions to ask, but after using the first two questions, they start to have a conversation and Cole asks another question without realizing it. Dandalus admits that it's hard to converse without them, but Cole doesn't need to worry about it because it only actually applies to the important questions, and he'll tell him if he hits upon a topic that requires him to use his third "official" one. He eventually does, wondering if Dandalus can help him get his power back, but Dandalus can't help, and he feels he's wasted his third question. At this, Dandalus looks around, comments that he doesn't see anyone else waiting and notes that the rule was only made to prevent frivolous inquiries. Obviously, Cole isn't interested in frivolous inquiries, so he's allowed to ask more questions. He ends up learning several more important things before they both agree that it's time for Cole to move on.
In the second Flat Stanley book, Stanley ends up being used as a sail in a boat race. A judge is heard saying that it is not against the rules to use your teammate as a sail.
In the Dale Brown novel Flight of the Old Dog, the Soviets refuse to shut down their Kavaznya laserCannon, claiming that the previous strategic arms treaties said nothing about ground-based laser systems. In Shadows of Steel it is said that while the USSR and China signed arms control treaties against selling to Iran, none of the other post-Soviet states did.
In the Clockpunk fantasy Goblin Moon, a friend of the heroine's aunt marries a criminal she's never met, just before he is executed for his crimes. She does this because she owes her creditors a fortune, which automatically become her husband's problem as soon as she weds him; as an instant widow, she's free of her debts and can go on to marry the man she actually loves. All the criminal gets out of it is the company of a prostitute and a bottle of wine for his last night, courtesy of a well-bribed jailer.
Gods and Generals has a couple of instances. Joshua Lawrence Chamberlain is given a two-year sabbatical in hopes that he'll go to Europe and get the war out of his head—instead he goes to the governor of Maine and gets a commission as lieutenant-colonel of the 20th Maine. In a separate incident, General Hancock is repeatedly ordered to retreat despite being in an excellent position to flank the enemy. When he's given a final warning by the messenger, Hancock makes his troops "withdraw" into the Confederates.
In book five, he bets Sweyn that he can catch a bigger trout with a pole, line, hook, and worm bait, than Sweyn can with his rod, reel, and fly hooks. Then he tells J.D. that there ain't no rule against setting up six poles at once.
In book seven, he bets that Parley Benson's quarter horse can't beat Sweyn's mustang in a mile race. He wins this bet easily since Parley's horse hasn't the stamina, then proposes to give the kids a chance to win their money back by swapping horses and racing again. When he wins on the other horse, the kids accuse him of cheating, and he tells them that there ain't no rule against slowing a horse to let it get its wind, and that if Parley had done it, they certainly wouldn't have complained.
In The Guardians, there ain't no rule that a Guardian can't become human, exercise human rights, and become a Guardian again. And they gain a second Gift upon their second self-sacrifice, which is why Michael has so many Gifts.
In Chamber of Secrets, it's revealed that Arthur Weasley works in the Misuse Of Muggle Artifacts Office, but abuses Muggle artifacts on his own time. He purposefully wrote a loophole into the law in order to get away with this, namely it is misuse to use said object to harm or mislead a muggle. Personal experimentation in one's own home is another matter altogether.
A house-elf can only be freed when their master presents them with clothes. At the end of Chamber of Secrets, Harry gives a sock to Lucius Malfoy (the sock is hidden in Riddle's diary in the film), who then accidentally gives it to Dobby. Since Dobby was "presented with clothes", that means he's a free.
In Goblet of Fire, the rules for the first contest states that contestants can only bring a wand to face the dragons, but not that they can't use it to summon whatever else they need. Harry uses that loophole to summon his Firebolt flying broomstick.
In Order of the Phoenix Kreacher deliberately misinterprets Sirius' command of "Get out" at Christmas to leave Order HQ and make contact with Narcissa Malfoy. While Sirius' orders prevent Kreacher from relaying information on the Order's activities to Voldemort, he's still able to give intel that Sirius didn't consider important enough to classify namely that Harry loves his Godfather and would go to any length to rescue him. This is key to the trap Voldemort lays in the Department of Mysteries. On a lighter note when Fred and George start selling their Skiving Snackboxes after demonstrating them in the common room, Hermione can't do anything about it because they're free to test the products on themselves and it's only against the rules for the two to sell them if they're dangerous (which is proven not to be the case).
Also in Phoenix, Umbridge has the Ministry enact many executive orders to suppress questions and discussions of Voldemort's return. One of the orders is that teachers cannot discuss anything with their students that is outside their respective subject matter. When Fred and George make their epic exit from Hogwarts, the teachers send Umbridge running around the school to remove all the fireworks that have scattered throughout the castle. Flitwick says he could easily have done it himself but wasn't sure if he had the authority.
Late in Prince, Dumbledore takes Harry to a cave he believes Voldemort had hidden a Horcrux inside, at one point reaching a lake with a boat. Dumbledore deduces that only a fully grown wizard is able to ride in the boat at a time, but Harry is able to ride alongside him since Harry himself is 16 at the time and, therefore, still too underage to qualify as a fully grown wizard.
Deathly Hallows: The Elder Wand has passed from hand to hand when the previous owner is killed. Voldemort assumes that this is the only way to gain control of it. It's not. More specifically, it's only necessary to defeat/disarm the previous owner. Voldemort assumed that the Elder Wand had "passed to" Snape when he killed Dumbledore, but Malfoy disarmed him first, and when Harry later defeated Malfoy, the Elder Wand recognized him as its master. Even more specifically, ownership is passed only when the current owner is 'defeated/disarmed'. Dying without either of those conditions being met or arranging for one's suicide, even by help of another, means there is no transfer of ownership of the wand and its true power dies with the last owner. Dumbledore knew this, hence why he arranged his Mercy Killing with Snape. Malfoy was simply a Spanner in the Works in that regard. Ironically, Voldemort's investigation led him to the two people who held the Elder Wand before Dumbledore, and both of them were still alive, so he could have easily realized that the killing clause was incorrect.
Quidditch defies this trope by having a rule for everything. For example, there's a rule that forbids using a battle axe in play and that's just the tip of the iceberg. According to Quidditch Through the Ages, these rules arose because of this trope, and the full list of rules is kept hidden so as to prevent anyone from getting ideas.
The Hearts We Sold: It's rumored that if you can find a loophole in your deal with a demon, fair and square, they'll let you go. It's true. The Daemon accepts it gracefully when James manages to game the system, releasing Dee from her contract early. The Daemon removes people's hearts, and needs heartless people to do work for him. Humans can't survive without a heart... but it doesn't need to be theirs. So James literally gives his heart to Dee, which kills him, but makes Dee useless to the Daemon, meaning he has no reason to keep her under contract.
Ain't no rule that a chicken can't be mayor. This one is from the book Herb Seasoning by Julian Thompson. Said chicken actually understands English and can write in (no pun intended) chicken scratch, but she's really being used as a figurehead for a conman. Long story, just read the book. Oh, and there Ain't No Rule that says the cure for depression can't be a mixture of eel slime and aspirin. Applied topically.
The Amazons get their queens crowned by fights to the death. Given the whole death thing, there's no law against repeat matches- so when an old queen comes back from the dead wanting a rematch (and being able to return even if she dies in battle), you can bet that Hylla was going to get out her law-fu ASAP.
The fourth book reintroduces Calypso and the island of Ogygia, which nobody can find any more than once in their lifetime. Leo, having fallen in love with Calypso, finds the solution: inject himself with the physician's cure after his Heroic Sacrifice in order to give himself a second lifetime and find Ogygia all over again.
In The Short Victorious War, Harrington learns the reason Young was not removed from command after the events in On Basilisk Station. He used a loophole to give his return to the shipyard for repairs a legal basis.
At the end of the prequel short story "Let's Dance!" from In Fire Forged, the First Space Lord has been pressured into relieving Honor Harrington from command of the Hawkwing for cooperating with the Audubon Ballroom to take down a slave depot. He proceeds to reassign her to the Advanced Tactical Course, also known as "the fast-track to senior command".
In In Enemy Hands, Thomas Theisman tries to appeal to the international law of the Deneb Accords to secure fair treatment of Prisoners of War from the otherwise sadistic Cordelia Ransom. Ransom uses his own logic to find a way to Loophole Abuse the Accords into letting her do what she wants anyway, only making it completely legal, and Theisman spends the rest of the night puking over what he's just unwittingly done.
Another loophole was used in the Andermani Empire following the removal of the mentally unstable Emperor Gustav VI. With no living brothers or sons, and a potential civil war on hand, his oldest sister had herself declared legally a man, took control of the navy and essentially dared any of her cousins to challenge her right to reign as Gustav VII.
This is how the Obstructive Bureaucrats of the Solarian League gained power: Their constitution gave every member nation of the League veto power over statutes... but not over regulations, which is what the bureaucrats used.
In Robert E. Howard's short story "The Horror From the Mound", Lopez swore inviolable oaths never to speak of the Mound's curse to anyone except his own eldest son. He never promised not to write down the secret so his neighbor could read it, however...
In the Imperial Radch short story "She Commands Me and I Obey", Breq captains a sports game with deadly high stakes when she learns that one of her teammates is being bribed to throw the game. She's not allowed to bench them, so she casually breaks their leg: attacking an opposing player is against the rules, but crippling your own teammate technically isn't.
In Inheritance Cycle: Oaths sworn in the Ancient Language technically cannot be broken. More broadly, it is impossible for a person to lie in the Ancient Language, so a person is compelled to follow through. However, the magical nature of the words spoken in the language are very subject to Exact Words, meaning that there are ways to get around this. Eragon himself inquires whether this means that the elves, who speak exclusively in the Ancient Language, never lie, to which he is told that the elves are experts in Double Speak.
If you know someone's true name, you can use the Ancient Language to compel them to do your bidding, but your orders have to be very specific. This was how Murtagh was able to allow Eragon to remain free at the end of Eldest "Galbatorix ordered me to try to capture you, and I did try." In latter installments, it becomes obvious that Galbatorix has modified his orders to prevent this sort of thing, but the fact that Murtagh is still able to flee at all indicates that the orders are now something along the lines of "Capture him if at all possible, but flee if you can if it becomes obvious you can't win at the moment."
This is later used to allow Eragon to forge a new Rider's sword, as the only blacksmith capable of doing so has sworn in the Ancient Language never to forge another weapon. Instead, she uses magic to manipulate Eragon's limbs to allow him to make it by proxy. This is acknowledged, as the blacksmith warns Eragon off of asking too many questions about it; it'll only work if she herself believes that it doesn't count.
It is later revealed that the restriction on lying in the Ancient Language does not apply to a falsehood that the speaker believes to be true. Meaning that if someone tells you something in the Ancient Language, it means that they firmly believe it to be true, not that it necessarily is. This is used as a plot point, as Murtagh's revelation that Eragon is the son of right-hand man of the Evil Emperor is delivered in the Ancient Language. It's not actually true, but Murtagh certainly believed that it was.
I, Robot: In the story "Little Lost Robot" notes that the ".. or through inaction.." clause of the Three Laws was added prevent a different Loophole Abuse, where a robot could push a heavy box onto a human from above if it knew itself to be capable of later preventing it hitting the human - arguing that the action of pushing therefore had no certainty of causing harm - but then not actually save the human, since their compliance with the law was fully satisfied by pushing the box. The clause was problematic, as it resulted in robots spontaneously grabbing humans and pulling them out of even regular X-ray machines, since the robot could not be certain how long the human would be exposed for and even a short-duration exposure causes some amount of "harm", even though it is insignificant if managed correctly.
Johannes Cabal the Necromancer: Johannes wagers that he can collect 100 souls for Satan in a year, regaining his own soul if he wins or dying if he fails. When he falls one short, he points out that their deal only requires him to hand over the souls if he wins and that he has nothing left to lose by defying Satan out of spite. Satan crossly accepts the lesser number and still falls for Johannes' Kansas City Shuffle.
The Kid Who Ran For Principal by Judy K. Morris. Ain't no rule that says a student can't run for interim principal for the purpose of firing an ineffective and cruel teacher.
The Last Days of Krypton: Jor-El tries to get around a ban on space travel by building a device to explore worlds in other dimensions, accidentally discovering the Phantom Zone.
Macdonald Hall: In The Zucchini Warriors by Gordon Korman, Cathy from the girls' boarding school across the street pulls a Sweet Polly Oliver and serves as quarterback, leading the team to victory. Naturally, once it's found out, the team coach attempts to argue that girls can too play football (despite having said in a prior interview that they can't). The referee shuts this down by pointing out that, as this is the Macdonald Hall football team and Cathy is not a student there, she's not eligible to play.
In the Mickey Haller book series, this is Mickey's bread and butter. While he will not break the law, he definitely has a startling ability to get around it. For example, in order to influence witnesses he has:
Used a former client of his to plant some testimony with a witness that was in the same drug program.
Brought in a former associate of a current witness into the courtroom. This causes the lying witness to stop answering questions as he thought his former associate could impeach him and his testimony (though this was not the case).
Managed to subpoena witness to the stand, only to force him to take the fifth in front of the jury in order to bolster his case.
Faked a fight in a courtroom, forcing a mistrial and ensuring that the witness who was there would be too scared to come to a retrial.
The Murderbot Diaries: This is how the titular artificialCyborg can travel freely through the setting despite legally being property. For example, AI-piloted spaceships are told not to give information to random humans, but not how to respond to a friendly fellow AI who asks to be allowed onboard.
Jim C. Hines' Princess series used this in the final novel, The Snow Queen's Revenge, for the character of the Duchess, a powerful fairy who got out of her execution after she tried to kill the King and Queen of Fairytown by asking to see one last sunrise before she died; she subsequently fled underground where she could not see the sun, allowing her to do basically whatever she wants so long as she does not come into direct contact with the King and Queen or directly antagonise human royalty. The Duchess also plans to take Jakob, the son of Danielle- AKA Cinderella- and make him her own protégé by making a deal with Danielle where she would help Danielle in the current crisis in exchange for the Duchess having half the year with Jakob until he became an adult. With Danielle fully aware that time passed differently in Fairytown, and therefore 'six months' could equal several years where the Duchess would have time to manipulate Jakob and turn him against his family, Danielle gets around this by marrying Jakob to Greta- the 'sister' of Snow White- which makes him an adult by the law of her kingdom, and subsequently uses a complex spell to show the Duchess a magical recording of a sunrise, allowing Fairytown to take her into custody.
Used in Robert Asprin's Phule's Company, when the company competes on an obstacle course against the elite Red Eagles. The race specifies "full combat gear and conditions", and the Eagles make good time navigating the obstacles in heavy packs with loaded weapons. Then on their turn, Phule's company blows up the obstacles, and sprints straight through in record time. Some Eagles complain that this is cheating, but their own commander agrees that in "combat conditions", you're not worried about being polite to the landscape.
Rachel Griffin: In The Unexpected Enlightenment of Rachel Griffin, Rachel and her cohorts have a pressing need to get to the infirmary; but, students are not allowed out of their dorms after curfew. There is no rule that says you can't put yourself in the infirmary by having your friends punch you repeatedly.
In the Rainbow Magic series, the second series published, the Weather Fairies, has this. Jack Frost promised not to harm the Rainbow Fairies at the end of their series... so he harmed the Weather Fairies instead.
In the children's novel Ralph S. Mouse by Beverly Cleary, Ralph's human friend, having discovered Ralph and his comparatively impressive intellect, decides to bring him to school for show and tell. The children decide to test his smarts by putting him in a maze with some food at the end and seeing how long it took him to get to the food. Ralph decides that the whole thing is stupid, climbs up the wall, and runs along the top of the maze to get to the food quicker. The children call loophole abuse, but instead of forcing the issue by covering the maze, they just put him back at the beginning, allowing Ralph to repeat his stunt over and over until the children get fed up and declare that, far from being smart, Ralph is too stupid to complete the maze by following the rules. Ralph and his human friend find this an unfair assessment, since they asked Ralph to get to the food as quick as possible and Ralph delivered repeatedly.
In Marina Tsvetaevas The Rat-Catcher, a poem based on the legend of The Pied Piper of Hamelin, thats what the mayor uses against the piper. The decree states that anyone who drives the rats away, should he even be a demon, will get to marry the mayors daughter. When the piper asks about his reward, the mayor says that the decree mentions a demon, not a musician.
In the first Red Dwarf book, Infinity Welcomes Careful Drivers, it is explained that after the advent of genetic modification, specially created athletes were designed for their league games with their entire bodies suited for their role - twelve foot basketball players, boxers with heads of unthinking muscle and so on. One football (soccer) team fielded a goalie which was a massive oblong block of flesh that filled the goal mouth. Somehow they still failed to qualify for the second round.
Redwall: Matthias, at the top of a bell tower, promises Big Bad Cluny he'll come down if Cluny releases his hostage. Ain't no rule that Matthias couldn't cut down the giant bell, which Cluny is directly under, before coming down.
Raymond E. Feist's The Riftwar Cycle: Early in Daughter of the Empire, the main character, Mara, is attacked by an assassin on a spot in her home that, under the law, only members of her family can go on pain of death. She's rescued by a soldier but, even though he saved her life, he still needs to be executed for trespassing. She declares that he will be executed... someday, at an undetermined point in the future. This basically lets him off completely and it also means that, since he's technically a dead man walking, he can get away with things (like manhandle an irritating nobleman), that would ordinarily get him killed on the spot. In fact, the core concept behind Mara's rise from minor noblewoman to the most important person in the Empire was her realization that violating tradition wasn't illegal. This allowed her to recruit a large number of people who were traditionally required to act as outlaws, but had never technically been outlawed, such as hundreds of highly competent soldiers whose masters had been killed and the head of the Empire's top spy network.
In The Rithmatist, Joel spends a lot of time at the start of the book trying to get into Rithmatics classes despite not having the magical aptitude to be a Rithmatist. When he tries to get a summer elective with Rithmatist Professor Fitch, Principal York tells him that there are rules against normal students taking Rithmatics classes and that's that. He then mentions, as if off-hand, that Fitch had just been assigned a new research project that would last the whole summer, and would probably benefit from the help of an enthusiastic young lab assistant.
The Robert Ludlum novel The Road to Omaha has half-mad General Hawkins using an old treaty to bring a case right to the Supreme Court that demands the U.S. government return all lands stolen from the Wopotami tribe...which is basically the entire state of Nebraska including the Strategic Air Command. At first thinking he's insane, the other characters have to marvel at how well Hawkins is able to work the law.
Charlie Sunset is a Wopotami lawyer who creates the brief for Hawkins, thinking the whole thing is a lark as it will take years for this case to work its way through the lower courts. Too late, he realizes that because of the wording of the treaty and how it counts as a massive robbery by the U.S. government, Hawkins can circumvent the entire circuit system to have this heard directly by the Supreme Court in just a few months.
Charlie uses this to escape this madness. He points out that while he technically has passed the Nebraska bar, it will take months before they finally give him full credentials as a lawyer that he can present. This means there's no way he can argue in front of the Supreme Court as it would disqualify the entire case. Hawkins decides to hire on old "friend" Sam Devereaux.
Early in the book, Aaron Pinkus confronts Sam on how he and Hawkins kidnapped the Pope in the prequel book The Road to Gandolfo. Sam states that kidnapping is defined as "holding someone against their will" and as it happens, the Pope actually enjoyed this "vacation" and was downright happy to go along with it.
Sam adds that he had a fake corporation set up to handle the whole thing which had its stated purpose being "the handling of acquired religious artifacts." Aaron has to acknowledge that kidnapping the Pope would count as that.
Charlie's sister, Jennifer Sunrise, is upset that her tribe is being used for this and demands Hawkins stop it. Hawkins appears to agree and vows he will abide by the wishes of the Tribal Council. Jennifer then gets a frantic phone call from her brother telling her that Hawkins has bribed the Elders with a million dollars (with the promise of millions more once the suit is won) to convince them to make him arbiter of all tribal affairs.
Jennifer: He told me he would abide totally by whatever the Council of Elders approved!
Charlie: Why not? He is the Council of Elders.
Jennifer is irate but Aaron walks her through the agreement to determine that Jennifer herself gave the Elders this power as a point of pride, never thinking they'd do anything without her permission and there's no way she can overrule them. The Elders were clearly of sound mind enough to not only accept the money but invest it and cut Jennifer and Charlie out of the deal. At worst, Hawkins merely didn't tell them what he was planning to do and they never bothered to ask. As Aaron points out, ignorance and/or lack of communication between friendly parties is not proof of fraud and if Jennifer tries to stop it, it will look as if she's trying to get her hands on the millions of dollars Hawkins is promising to earn the tribe over the lawsuit.
Jennifer: It's crazy!
Aaron: Crazy as a hawk. In another life, the General would have made a superb corporate attorney.
Richard Marcinko of the Rogue Warrior novels claims to really have recovered stolen nukes, and saved London from a biological attack, and take down a Presidential candidate, stopped Russian and Chinese hardliners, etc. But the Navy won't let him write those exploits so he writes the stories as fiction.
In the Safehold series by David Weber, the heroes relentlessly exploit loopholes and creative interpretations of the religious prohibitions concerning technological advances.
One of the more notable examples of outright abuse comes with explosives and chemistry: the "archangels" who created the rules couldn't explain why certain things shouldn't be done (since that would expose people to too much knowledge), only saying that mixing chemicals X and Y would result in dangerous, magical retribution. If, however, you wanted that "magical retribution" to occur in certain controlled conditions, say in a fuse attached to a gunpowder-filled artillery shell...
Gets even better when one of the people directly responsible for enforcing the restrictions gets brought in on the secret (namely that the religion in question is a Path of Inspiration) and starts helping the heroes abuse loopholes. Naturally having shot down attempts at loophole abuse in the past, he's well familiar with how that game is played.
Count Olaf of A Series of Unfortunate Events plans to marry his ward Violet to get at her inheritance. (And, it is strongly implied, some other things.) She's underage, so the marriage has to be approved by her parent or guardian. In this case, that would be Count Olaf. He stages the marriage in the guise of a play about a wedding, even tricking a judge into performing the ceremony, with the audience as witnesses. Violet takes advantage of a loophole herself; the law states she has to sign the marriage license in "her own hand". She's right-handed, so she simply uses her left hand, making the marriage null and void.
The film version plays out slightly differently. Olaf caught the kids reading law books earlier in the film, and thus catches Violet's trick. After the contract is signed, he gloats about it. When Poe demands Olaf be arrested, the Baliff says, awkwardly, that the wedding was perfectly legal. Then Klaus uses the same device Olaf used to kill the Baudelaire parents to set the contract on fire. The audience then arrests Olaf.
Shadows for Silence in the Forests of Hell: It's forbidden to spill blood in the Forests, since it enrages the deadly, undead wraiths that infest the region. Killing people in other ways — even by sticking them in a waterproof sack and bludgeoning them to death — doesn't draw their attention in the same way that a single drop of blood can. Exploited both ways by the Bounty Hunter Silence Montane, who kills her marks bloodlessly and uses a single drop of blood to doom the Big Bad.
A Simple Survey: This is frequently employed in the second volume. Some examples include:
A modified game of hide-and-seek, with five hiders and five seekers. The hiders have 30 minutes to hide (in an abandoned amusement park), and the seekers have 30 minutes to find them. The seekers win if they find all of the hiders within the time limit, otherwise the hiders win. There's no rule saying all of the hiders have to be alive at the end. The narrator kills another hider and dumps her body in the aquarium, where no one would think of looking, allowing the hiders to win.
Five people are each given a gun with one bullet, and told that the last person alive wins. There's no need to actually kill any of the other contestants. The winner is the one who fakes their death at the beginning, by changing his bullet into a blank and pretending to accidentally shoot himself. The other contestants kill each other off, never realizing that he was still alive.
In Skulduggery Pleasant: Kingdom of the Wicked, Skulduggery need to obtain information from the Dimension hoppingSerial Killer Silas Nadir. Upon heading to the prison he is in, they find out that he's spent 15 years hooked up to an illegal machine that's been using his magic to move the prison through dimensions every second, while at the same time keeping him comatose and unaware that time is passing. Naturally, Silas would prefer to spend his prison sentence in a machine that can make decades feel like an instance, so he refuses to divulge any information unless the Grand Mage signs a form stating he has to spend his sentence attached to the machine. Silas gets the official form he requested - but it's only after he's divulged information that he finds out the Grand Mage fifteen years ago is long dead, and the current Grand Mage signed the paper in his predecessor's name, making it invalid.
Cobb is able to let Spensa into flight school because he has the final authority over who is in his class, and even the admiral can't override him. She fights back by refusing to let Spensa use anything but the classroom and the training ships, locking her out of the mess hall and the dorms.
M-Bot cannot disobey his pilot's orders, even centuries after that pilot is dead. But he was able to sneak a subroutine in and, when his main program wasn't looking, change who his pilot is.
Robin Hobb's The Soldier Son: One of the final exams in Shamans Crossing is a test of bridge construction. Turns out the actual test was simply "get your team across this river", which is most easily done by making them all swim. Nobody said making a bridge was mandatory.
Also happens near the end of her Fool's Fate, where Dutiful technically fulfills the terms of his betrothal to Elliana. The price demanded the head of the dragon Icefyre, laid upon the hearth of her family's stronghold; the expectation was that it be severed, but when an ancient and very much alive dragon sticks his head through your wall as a minor favor to the people who helped free him, not many people seem to want to argue the point.
In A Song of Ice and Fire, the laws of hospitality are sacred in Westeros. Not so much any other laws; when the legendary Rat Cook served a king his own sons in pies, there was no problem with the murder and cannibalism parts; he was condemned (and cursed) only because they were his guests. As such, when Lord Wyman Manderly desired to take Revenge with a capital R on the Freys and Boltons and decided to emulate the Rat Cook, he carefully waited until his Frey guests were leaving, gave them gifts which formally marked their departure, and thenhad them murdered, made into pies, transported to a feast hosted by the Freys and Boltons, and served up. He ate several slices himself, with relish.
Similarly, the Dothraki have a holy city named Vaes Dothrak, wherein no Dothraki may wear a blade or shed a free man's blood. As such, supposedly some khals employ men to strangle people with silk, which doesn't shed blood. Viserys Targaryen wears a sword, claiming that since he isn't a Dothraki it's not a problem (though this may not actually apply). Khal Drogo then kills him by pouring molten gold on him, which again doesn't spill his blood.
While it never goes off, Arianne Martell's scheme to crown Myrcella has this as one of the legal excuses — by Westerosi law, females are placed far back in the line of succession — but when Dorne joined the realm of the Iron Throne, part of the agreementnote since they were not conquered but rather joined via marriage alliance was that Dornish law applies in Dorne, and Dornish law does not care about gender when it comes to succession, unlike all other six Westerosi kingdoms.
After rescuing Jaqen H'ghar and two other prisoners from death, Arya Stark is offered three deaths — no more, no less — if she'll just give him the names. When he leans on this to deny Arya help in escaping captivity, she threatens to have his name be the third to force the issue.
Also, the reason why the Night's Watch recruits frequently visit the whorehouse in Mole's Town: the oath says that they will have no wife nor children, but it says nothing about having sex.
Spinning Silver: Miryem stakes her life on a magically binding wager with the Staryk King that she can turn the silver in his three Treasure Rooms into gold within a time limit. It's far more than her magic can transmute in time, so she has several allies sneak the silver from the third room out a back exit — once it's not in the treasury, it doesn't count. Both the King and the magic of the wager accept this.
The Thrawn Trilogy: Palpatine, as he fell to his death on the second Death Star, put a compulsion into the mind of his Emperor's Hand, Mara Jade. "YOU WILL KILL LUKE SKYWALKER!" In the third book of the trilogy, Mara purges the compulsion by killing not the original Luke Skywalker, but Luuke Skywalker, the evil clone created from Luke's hand that was lost at Bespin. There was no rule that it had to be the original Luke Skywalker she killed.
Edgedancer: Nale's unable to do anything illegal, but needs to kill a magic user who didn't commit any crime. Turns out it's not illegal to pester the local prince to change the law - so this is what Nale does. Considering that the magic in question is barely more than a myth at this point, it's likely that the prince only agreed to get the crazy guy to leave him alone.
A test for novice Skybreaker Magic Knights — an Order devoted to legalistic Honor Before Reason — has them flying around a playing field, trying to hit each other with pouches of coloured dyes, with victory going to whoever has the cleanest uniform at the end. Szeth wins by washing the dyes off his uniform in the last few minutes.
Somewhat similar instance in Stuart Little, where Stuart and George realize there's no rule against a mouse sailing one of the racing boats.
In her Tales of the Five Hundred Kingdoms novel Fortune's Fool, Mercedes Lackey uses an ifrit as the villain. At the end, the ifrit is bound into his bottle. But the bottle cannot be sealed permanently; there must be a release condition, and it must be possible, however unlikely. So the ifrit is bound into the bottle "until you repent and reform and join the ranks of the Lawful Jinn of the City of Brass!" Geniekind have free will, he can choose between good and evil.
In The Tamuli, it turns out that the situation with the Delphae is this. They're cursed, all right... but the local rules of magic don't actually specify that there has to be a real downside to the effects of a curse. Since enchantments reveal their presence to anyone with magic, while curses are so quiet as to dampen the 'sound' of any magic done in connection with them, being 'cursed' serves the Delphae, who want to hide from the rest of humanity, well.
When the Hot-Blooded dragon Iskierka learns that British dragons have limited legal rights outside their role as Sapient Steeds for the Aerial Corps, she starts leading unmanned raids on enemy ships; since there are no humans to contest her claim to the prize money, she soon amasses much more capital than her nominal master.
When he's brought in to reinforce the badly uncoordinated Russian army, Laurence can't pull rank on them as an adoptive Prince of China without staging a formal state visit. Putting his half-Nepalese friend in ostentatious robes, announcing that a Chinese Prince has arrived, and letting the Russians draw their own conclusions isn't explicitly forbidden, so they do that to get hustled straight into the command tent.
In the Thursday Next novel Something Rotten, ain't no rule saying a genetically re-engineered Neanderthal can't play croquet although it was in dispute; there are rules saying non-humans can't. The rule that non-humans cannot play croquet would normally have prevented him from playing, but the reconstruction involved using some human genes for the vocal cords. As a result of the small percent of human DNA, he wasn't technically non-human, so they let him play.
In the Next-World's version of croquet, finding loopholes in the rules is an expected part of gameplay and heartily enjoyed by the fans.
Treasure Island: During his confrontation with Israel Hands, Jim Hawkins manages to prime his two pistols while Hands is still too far away to stab him with his dirk, and tells Hands in no uncertain terms that he'll shoot if Hands comes any closer. Hands responds by throwing his dirk at Jim.
Troy Rising: In Citadel, a junior welder places a fake spider in the work sled of a hated coworker shortly before he goes out on EVA. When questioned about it, it is pointed out that there are regulations about tampering with a coworker's spacesuit, but not about the sleds. It is strongly implied that the safety regulations in question are rewritten after that incident.
In the novel Vampire High, a group of vampire students decide to join the water-polo team and take their school to its first-ever victory...and then it turns out that these students have a strange and rare gene that lets them become seal-human hybrids when in the water. With their enhanced strength and speed, they win the game by a two-hundred point margin, and a group of lawyers present protest, saying that the rules state only a human can play on the team. The protagonist's father tells them that "The law hasn't quite decided what is and is not human," and points out that there were other vampires on the team who didn't have the gene, and no one had complained. The lawyers persist, however, until the protagonist's father tells them he's a lawyer in a VERY powerful and influential firm, and the guys back off.
A story by Brazilian writer Luis Fernando Verissimo has a couple who returns from honeymoon only to get divorced. The guy explains that in-between the sex, they played pen and paper Battleship. After hitting the girl's aircraft carrier, somehow the four nearby spots were misses. She explained that she broke the ship in four parts and spread them across the board! His friends agreed that someone like that couldn't be trusted... and he didn't even tell of another cheat, where she didn't put the submarines in the map because "they're so deep not even I know where they are".
It is a frequently cited legal precedent that there ain't no rule a horse can't be a count's heir (or at least, there wasn't in Lord Midnight Vortala's time). If a horse's ass can be a Count, why not the whole horse? Though the horse died and the count's human son reconciled, it actually established an important legal precedent; a non-blood relative can be designated a Count's heir.
On the other hand, while each Count can only legally have 20 of his own troops, total, there Ain't No Rule against a Count hiring 2000 chefs, equipping them with Chef's knives and sending them after his enemies. The Emperor was not amused, and sentenced him to publicly starve to death. Luckily, an invasion happened, and he was allowed to regain his honor and died in battle.
The POW camp in the short story The Borders of Infinity applied this trope in a rather nasty manner. So many square meters per inmate? An opaque, luminous force shield encloses that much open ground and field latrines. No periods of darkness for over twelve hours? No darkness at all, ever. Water? Everyone gets a cup along with their clothes and a bedroll (the taps by the latrines work most of the time). Access to medical personnel? Plenty of medics mixed in with the general population, but they mentioned nothing about equipment. Food? A pile of ICRC-equivalent compliant ration bars (one per inmate) appear at a random location on the camp perimeter twice per day. No solitary confinement for more than 24 hours? <insert bitter laughter here> No beatings or rapes by guards? No guards....
Part of the backstory of David Gerrold's The War Against the Chtorr series is that the United States had severe arms limitations imposed on it after the last world war. There was no such restriction on weapons research. Therefore, the U.S. funneled tons of money into advanced weapon design programs and built modular factories that could be turned to war production with the flip of a switch.
Aes Sedai are bound by the Oath Rod "to speak no word that is not true," but the Oath Rod defines "true" as "what the speaker believes." Thus, an Aes Sedai who believes a lie can tell it as if it were the truth, and the Aes Sedai are experts at using this and other Loophole Abuses to twist the truth beyond recognition.
The third Oath "Never use the One Power as a weapon, except ... to save her own life, or her Warder's, or the life of another sister " can be circumvented by an Aes Sedai intentionally placing herself (or, presumably her Warder or another sister) in danger. The danger has to be real and fatal, though (or at least the sister has to believe it is), meaning they can't exactly use this loophole to shatter armies with impunity the way they could without the Oath. The spirit of the law is upheld.
In The Gathering Storm, it is revealed that one of the oaths the Black Ajah swears to the Dark One is "I swear not to reveal the Black Ajah or its secrets until the hour of my death." One recruit forcibly drafted into the Black Ajah learns everything she can about its members, leaders, plans, and prophecies, then proceeds to betray it to Egwene by taking poison first. One would think the Dark One would close this loophole, but as Egwene herself says, "What kind of Darkfriend would kill themselves in order to advance the greater good? It doesn't seem the kind of thing his followers would consider."
Under Tower Law the Amyrlin must be Aes Sedai, but you don't have to be Aes Sedai to become Amyrlin. Thus, raising Egwene as Amyrlin makes her legally Aes Sedai without having to raise her as Aes Sedai. For even more bonus points, they wouldn't legally have been able to raise any regular Aes Sedai without an Amyrlin.
The Eelfinn did this to Mat, when he unwittingly made his Three Wishes to them: "Wise to ask leavetaking when no terms were set, yet unwise not to set the terms. We will set the terms..."
Mat's foxhead medallion worked on a big loophole (proving the Eelfinn would have had a ball with D&D wishes) in that he was free of the One Power , in that the threads melts when they touched him directly, but if you picked up a pile of dung, for example, and threw it at him with the power, it still worked.
Mat, sadly, didn't learn his lesson well enough: in Towers of Midnight, he carefully binds the Eelfinn in a promise not to attack his party. Then there's a solid Oh, Crap! moment when the packs of armed Aelfinn show up to block the way out.
After Cadsuane makes a serious error, Rand orders her not to let him see her face again, on pain of death. Rather than get the message and leave town, she spends the rest of the book lurking among his retinue In the Hood. Even Rand privately lampshades her audacity.
In the Seanchan Empire, it's forbidden on pain of death to spill even a single drop of a noble's blood. As such, nobility are executed by coaxing them into a large silk sack and then hanging the sack off the edge of a tower until it rots away.
In The Witchlands, the Truce states that no side can destroy or loot vessels of another side. Vivia gets around this by taking enemy ships over without damaging them and changing the flag to her own before taking the ship to Lejna and unloading the cargo peacefully.
The land of Xanth has a law stating that the king must be an adult Magician and forbidding ruling queens. However, in Night Mare an enemy is incapacitating kings one after another and they're running out of Magicians... until one of the heroes decides that if a Sorceress is really just a female Magician, there's no rule that they can't have a female king. They continue by first pointing out that there is no proper definition of Magician other than official recognition, allowing lesser talents to be king, and eventually point out that nobody said the King of the Humans actually has to be human themself, which ultimately results in the equine Night Mare Imbrium very briefly ruling as King of Xanth until the crisis is resolved.
The plot of The Betrothed, set in the Duchy of Milan from 1628 to 1630, hinges on this: at the time Catholic marriages had been regulated since 1563 by the Tametsi decree, that explicitely forbade any external party from imposing or vetoing a marriage, but the decree had the giant loophole of being valid only in parishes where it had been published (something that would be patched up only in 1907 by the Ne Temere), thus don Rodrigo could exercise his traditional right as feudal lord to forbid a marriage in his domain and ordered don Abbondio, the local priest, to not celebrate Renzo and Lucia's wedding.
Agnese, Lucia's mother, suggests to get around Don Rodrigo's veto by having Renzo and Lucia go to don Abbondio with two witnesses and declare themselves man and wife, as in the end in Catholic marriage the priest is simply another witness, just the one of the minimum of three cited by name. By that time this trick should have not been possible, as canon law declared that wedding banns had to be read first... Except this addition came again from the Tametsi (indeed, blocking this practice was the main reason it had been promulgated). Don Abbondio is horrified when Renzo presents him Lucia as his wife, and has to throw a carpet at Lucia before she can declare Renzo as his husband and run away while everyone's still surprised to prevent the marriage.
The Lies of Locke Lamora: Subverted. It is well known that the Bondsmagi will stop at nothing to utterly destroy anyone who kills a Bondsmage, so when Locke and his friends. are compelled to take vengeance on a Bondsmage, they take the mage's fingers, tongue and familiar, but are very careful not to kill him. It turns out that while this doesn't cause the organization to pull out all the stops the same way, the mage has enough friends and family to make Locke and his friends' life a living hell, and since Locke took the mage's fingers and tongue and thereby his ability to work magic (which they consider a Fate Worse than Death), they consider themselves fully justified in doing so.
In the Warrior Cats book Crowfeather's Trial, Crowfeather orders Hootpaw not to come with him to find Nightcloud, and not to tell their Clan leader Onestar what was going on. Hootpaw then returns with his new mentor Gorsetail, pointing out that Crowfeather told him not to tell Onestar, and that he can come along if his mentor gives permission.
Jarlaxle in The Legend of Drizzt series often required dealing with the most powerful (and temperamental) Drow in the city of Menzoberranzan who rely on him for information and additional manpower. Every conversation with one of these powerful Drow is met with numerous detection spells to root out if Jarlaxle is lying to them. The spells never help as Jarlaxle uses a combination of Exact Words and this trope to not actually lie, but not give any information unintentionally. Usually in those conversations Jarlaxle gets more information out of the one he's speaking with than he gives, much to the other Drow's frustration.