"Meaningless, huh? WHAT DO YOU KNOW OF MEANINGLESS!? Spend most of your life ruled by another... watch your race dwindle to a handful... and then... tell me what has more meaning than your own strength!? I have in me the blood of a Saiyan Prince! He is nothing but a joke! Yet, I've had to watch him surpass me in strength... my destiny thrown to the wayside! He... he's even saved my life as if I were a helpless child. He has stolen my honor. And his debts... must be paid!"
A standard ingredient of The Summation in any Cop Show, Police Procedural, Law Procedural or Mystery of the Week. After the detective has shown without doubt who the killer is, the killer will launch into a long, self-righteous (or remorseful) monologue explaining why exactly they did what they did. This both serves as confession and allows the writers to explain how this solution to the mystery makes sense, even if it's often a "He called my mother a bad name, he deserved to die!" kind of sense. It's often the only way to make the perp's feelings obey the Rule of Perception, since they must be hidden until the crime is solved.
This is a good place for a We Are Everywhere moment.
The detective will often then give them a Kirk Summation in response, followed by whatever phrase they use to indicate that they're being arrested. If the detective is feeling nasty he'll throw in "The Reason You Suck" Speech.
It doesn't matter if the character's a timid librarian, a jolly bartender, a butch farmhand, what-have-you, when they are revealed to be the killer they all suddenly snap into the same cookie-cutter personality type: bitter, twisted loony.
In real life, many people confess to crimes and will happily talk about what they did even though all they should say "I want to see my lawyer".
Also in real life, a criminal that's cornered tends to do things like socking the other guy in the face and running away. This rarely happens in television, despite the detective being so often the only other person in the room with the criminal, and when it does, they are almost always caught after.
This tropes doesn't necessarily have to be applied in the interrogation room, however. It could be given by the killer when he thinks that he's got the Final Girl at his mercy, or when he's explaining his motivations to an accomplice. All that matters is that the killer explains just why he's committing his crime in the first place.
This trope can overlap with New Era Speech if the villain's goals are particularely visionary.
This trope is the intended result of The Perry Mason Method. It's often part of a Villainous Breakdown. The Hero might respond by saying Shut Up, Hannibal!.
Every episode of Detective Conan ends with one in which the culprit explains why he or she did it. Sometimes countered by a motive rant from another person that completely destroys their motives and breaks the culprit completely.
The Kindaichi Case Files also does so. More often than not, the rant makes the killer a lot more sympathetic than his/her actions do.
Kaitou Saint Tail has a tendency to make her "victims" go into Motive Rants when she escapes with their already stolen goods.
Light has one in the last episode of Death Note, which is also a bit of a Hannibal Lecture about how the world needs Kira and if they stop him the world will only go back to the rotten way it was, and Near is only chasing him for his own ego. The latter was actually true.
So was the former, at least about the world returning to its pre-Kira state — according to Ohba, crime rates went back up after Light's defeat, proving that it was only fear keeping people in line.
In chapter 385 of Bleach, Tousen finally cracks and explains his motives for betraying Soul Society and joining Aizen. By the way, the "cracks" part is appropriate; his Hollow mask cracks open right when his rant begins.
Tosen: What is justice!!? Is it forgiving my beloved friend's murderer!? That is surely good! It is a beautiful thing! Undeniably so! But is what is good the same as what is just!? No!!! Living peaceably without avenging the dead... THAT IS EVIL!!!!
Naruto: Itachi gives one to Sasuke in episode 136 of Shippuden. It's all lies, though.
Happens once in Rebuild of Evangelion 2.0: when Shinji almost trashes NERV HQ, Gendo explains why he's such a bastard: he believes that he can only achieve his desires if he's willing to sacrifice everything and use his own strength.
Gendo gets a good one at the end of the Evangelion manga as well. Notable because he does it after he saves Shinji from the soldiers instead of Misato like in the anime, and because he explains in a straightforward, non-symbolism laden manner exactly how he feels towards Shinji: he doesn't love him, he doesn't like him. He is jealous of Shinji because Yui loved him as well. This is different from his in-anime justification which is that he didn't think he'd make a good dad and thought that Shinji would hate him, a Self-Fulfilling Prophecy, but he never gets the opportunity to make the rant there.
Saten: Uh...what? Mikoto: Yeah, you lost me somewhere in the middle there.
An interactive Canadian museum exhibit about forensic science challenges visitors to solve a young woman's murder. If you correctly determine who the killer is and what evidence proves it, you'll get to see the killer's Motive Rant. It turns out the killer was the young woman's literature professor, who had plagiarized a novel written by a friend of the young woman's family and used the resulting success to build his academic career. When the young woman found out about it, she threatened to expose him, which would have ruined his career. She wouldn't stop hounding the professor, and he eventually became so desperate that he killed her to try and keep her quiet.
The Big Finish audio play Davros has a spectacular Motive Rant for the title character. Starts out as a menacing whisper, but at the end, well...
Davros: When I press this switch, I will die. The poison in that projectile injector will kill in a moment. It is a perfect, efficient, killing machine. It will be painless they say. They tell me they know the pain I am in, as if they could! And that just by pressing this switch I will end that suffering forever. They say I should be the one to do it, but they are weak. They can not bring themselves to look at me, let alone kill me! They hesitate, they fear me! Even when I'm like this, and they have their perfect, pure, strong bodies, they fear me! And well they should! I am no longer like them, I am above them! I have the ultimate power, the power of life and death! This... body, this... is my dominion. Mine to command, no one else's! I can sense them out there in the corridor, cowering. Not daring to speak. They are the frail ones. They are the crippled. They are the ones without choice. They! Will! Die! They will lose this war and they will die! I could join them in defeat and death, but if I survive! If I survive, something stronger will emerge. A new race, the supreme power in the universe! I will not press this switch, I will not cower, I will not die!I! will! not! die! THIS! IS! NOT! THE! END! THIS! IS! ONLY! (dramatic pause) 'THE BEGINNING!'
Jason: Is that what you think this is about? You letting me die?! I don't know what clouds your judgment worse: your guilt or your antiquated sense of morality. Bruce, I forgive you for not saving me. But why, on God's Earth..." (kicks open a door, revealing the Joker.) "...IS HE STILL ALIVE?!?"
Watchmen has one of the best Motive Rants of all time, where the surprise villain, Adrian Veidt, reveals his incredibly elaborate plan while ignoring three separate peopletrying to kill him in mid-sentence, and not only did he actually pull off his scheme thirty-five minutes before the heroes even arrived, he also convinces a couple of the heroes that since he's already pulled it off, they have to go along with it for the greater good.
He also wins badass points for not falling into the bitter, twisted loony pattern. He says the whole thing with incredible calmness and poise.
Extra points for not ranting his plan out while the heroes could still stop it; he'd already finished by the time they got to him. The rant was to buy time so he could find out if it worked.
Buffy the Vampire Slayer: In the "Family Reunion" arc of the Angel & Faith comic book, when Angel calls Willow out on wanting to involve Connor in her plans to restore magic, she loses it, bitch-slaps him, and calls him out on his ways before breaking down about how Earth is becoming a Crapsack World without magic:
Willow: "Don't you dare. Don't you dare try to say I'm like you! This is all your fault! Thinking you can fix things! Running blindly down any road that might lead to redemption! And you're doing it again! Never worrying about the consequences until it's too late! You're ruined everything, Angel!!" (beat) "Can't you see what were missing? How empty the world is? There hasn't been a decent song, movie or book, since we lost the Seed! Suicide rates are spiking! All over the world people are losing hope! It's just starting! It only gets worse from here! The world's dying and nobody will admit it! I need to save it. There's nothing more important. Why doesn't anyone understand...?"
A Few Good Men has a truly epic one as the climax of the whole film. It builds up as the defense attorney, Lt. Kaffee, needles Col. Jessup with clever lines and pokes holes in the cover story he concocted after issuing an (illegal) order that lead to an innocent soldier's death. Jessup keeps his cool and hand-waves the holes pretty deftly, up until Kaffee catches him in a contradiction of his own testimony and Jessup launches into the rant when he can't offer an explanation. This example is an interesting variation of the trope where it plays out the motive rant before the actual, literal confession: Jessup goes on and on about the why of it, without actually saying he did it, until he's so worked up that when Kaffee interrupts to ask him point-blank if he issued the illegal order, he blows up and shouts, "YOU'RE GODDAMN RIGHT I DID!"
The trope is basically lamp-shaded earlier, when Kaffee assures the rest of the defense team that he can get Jessup to confess on the stand; he knows the Col. wants to tell the truth about what happened because he thinks he's right to have done what he did.
A fabulous comedic one by Debbie Jellinsky in Addams Family Values. "So I killed. So I maimed. So I destroyed one innocent life after another. Aren't I a human being? Don't I yearn, and ache, and shop? Don't I deserve love...and jewelry?" Extra points because the Addams family being who they are, they are completely sympathetic to her psychotic rant the whole time, even chiming in with understanding comments and agreeing with her about her motive for murdering her parents as a child.
Jimmy Stewart gave a melodramatic but effective example of this in After the Thin Man, in which he plays a painfully bland "nice guy" for 90% of the film, only for us to watch his character flip out in a fantastic performance in the final denouement.
Averted in the opening scene of Keeping Mum; when the police question her about the bodies, she just calmly admits to it as if murdering them was the obvious solution.
Summed up rather nicely in this conversation between Gloria and Grace (the killer):
Gloria: You can't go around killing people just because you don't like them!
The following conversation between Detective Conklin and the elder Yakuza boss Sugai in Black Rain is a very effective example of a subdued rant.
Sugai: Sato. He might as well be an American. His kind only cares about money.
Conklin: Oh yeah, what are you in it for? Love?
Sugai: I was ten years old when the B-29 came. My family lived underground for three days. When we came up, the city was gone. Then the heat brought rain. Black rain. You made the rain BLACK. You shoved your values down our throats until we forgot who we were. You created Sato and the thousands like him. I'm paying you back.
"I see a place where people get on and off the freeway. On and off. Off and On. All day, all night. Soon where Toontown once stood will be a string of gas stations. Inexpensive motels, restaurants that serve rapidly prepared food, tire salons, automobile dealerships, and wonderful, wonderful billboards reaching as far as the eye can see. MyGod, it'll be beautiful."
Sgt. Waters has two very effective ones in A Soldier's Story:
Waters:Them Nazis ain't all crazy. Whole lot of people just can't seem to fit in to where things seem to be going. Like you, CJ. See, the Black race can't afford you no more. There used to be a time, we'd see someone like you singin', clownin', yassuh-bossin'... and we wouldn't do anything. Folks liked that. You were good. Homey kind of nigger. When they needed somebody to mistreat, call a name or two, they paraded you. Reminded them of the good old days. Not no more. The day of the Geechee is gone, boy. And you're going with it.
A rare non-villainous example with Mrs Lintott from The History Boys, addressed to her all-male class and colleagues.
Mrs Lintott: I'm reluctant at this stage in the game to expose you to new ideas, but having taught you all history on a strictly non-gender-orientated basis I just wonder whether it occurs to any of you how dispiriting this can be? [...] History's not such a frolic for women as it is for men. Why should it be? They never get round the conference table. In 1919, for instance, they just arranged the flowers then gracefully retired. History is a commentary on the various and continuing incapabilities of men. What is history? History is women following behind with the bucket.
There's a cut one of these in an alternate ending to The Burbs.
Dr. Klopek: You were not quite right about the suburbs. Here all you have to do is take one step out of line. You paint your house the wrong shade of pink, you buy the wrong kind of car, you make one or two human sacrifices...Then when you walk down the street, everybody says "Oh, there goes the weirdo!"
Ray: Why did you come here?
Dr. Klopek: I came as you did. For the quiet! For the privacy! The good life! The convenient shopping with always plenty of ample free parking! But everywhere I always met all this suspicion and distrust!
Hans: It's true. In L.A. no one ever said anything!
Halloween III: Season of the Witch has a classic one from Conal Cochran, although it's not so much a "rant" as a "calm explanation" of his plan to use rigged Halloween masks to horrifically slaughter children across America.
I do love a good joke, and this is the best ever. A joke on the children!
M. Bison in Street Fighter questions why the heroes oppose him, and delivers this in the form of an epic speech to his underlings about his plan to unite the world in peace with an army of Super Soldiers.
In Man of Steel, Zod has two: one where he tells Jor-El how he's going to save Krypton. And the second has him tell Kal-El how he's going to kill every human he finds in revenge for Superman taking his purpose in life.
In Transformers: Dark Of The Moon, Sentinel Prime's motivation for siding with the Decepticons is so that he can restore Cybertron to its former glory. But it involves enslaving the human race as slave labor as part of his plan in rebuilding Cybertron, and to feed his own God-complex.
The Duumvirate asks for this before they kill important enemies.
Smerdyakov launches into one of these when he's finally questioned hard enough by one of the characters near the end of The Brothers Karamazov. He's not self-righteous or loony about it. He actually comes off as calm and collected, as if what he did is the most natural thing in the world. Given all the rants and profound conversations we've experienced thus far, he's almost justified.
Played straight, justified, and used to incredibly disturbing and offensive effect in Gaudy Night, the penultimate Lord Peter Wimsey novel and arguably the only one where the villain is ideologically motivated.
Since Tang Chinese law required the criminal to confess for a conviction, Judge Dee listens to a lot of these.
Played straight by The Mule when he gets caught in Foundation and Empire, then subverted as he proudly points out that while the conditions of this defeat have bummed him out and denied him the chance to eliminate a powerful potential enemy, he hasn't lost anything and in fact still has the upper hand. Then he just leaves because he has a galaxy to rule.
The villain of The Name of the Rose by Umberto Eco gets an extended one, in which he explains in detail why he was willing to kill to keep a lost Aristotlean book about laughter hidden.
The thief of the Scone of Stone in The Fifth Elephant gets one. The fact it's a dwarf who was upset with the Low King's liberalness when it came to things like openly female dwarfs was perhaps predictable, the final "Why should they be allowed to do this? I can't!" was less so.
In John C. Wright's The Golden Transcendence, Unmoiqhotep gives a multi-page, firebreathing rant on why he/she felt like destroying society...and is unpleasantly surprised to find that no one cares.
Subverted chillingly in Benito Cereno. When the instigator of the slave revolt aboard the ship is eventually found out, he never speaks a word about his motivations or tries to justify his actions.
Howard Roark has kind of the most epic one ever in The Fountainhead when he explains to the court why he destroyed the Cortlandt Homes project. It goes on for pages and pages. And he says it all incredibly calmly and matter-of-factly.
The killer in Perry Mason almost always does the motive rant on the stand, after which all charges against Perry's client are dismissed. You can tell the exact instant the culprit will stop denying and begin the motive rant based on the music changing. It is so necessary to the formula for the motive rant to occur on the stand that you can identify the killer instantly when Mason reserves the right to recall a witness.
Averted in one episode of CSI: Miami. At the very end of the episode, as a serial sniper is being taken away by the police, he asks Horatio "Don't you want to know why I did it?". Horatio simply replies "You're evil, you enjoy death, I hope you enjoy your own."
Also averted in an episode of CSI: New York. The killer seemed to have no real connection to the victim, who was a young woman in her early twenties, and he didn't tell them why he did it. Lindsey, who was shaken up because of the fact that she shared the victim's age and home state, visited him in prison just so she could ask him again why he did it. He just asks her "You came here just for that?" and puts the phone down.
Defied in an episode of Bones; when the criminal started explaining exactly why he'd turned to cannibalism, Brennan promptly knocked him unconscious, saying that nobody wanted to hear the "psycho speech."
iCarly: Missy gives one to Sam, as part of her latching onto the Villain Ball. It ruins the plan because it turns Sam from questioning if Missy even was trying to get rid of her, into sure of it, and decided to bring Freddie in to help her.
Every Law & Order. SVU really stretched it when a ten-year-old had such a rant explaining his motivation (it was 'cause he saw it on TV, see). Like in Perry Mason, the background music is often the cue.
Interestingly used on an episode where a man is on trial for manslaughter; specifically, he a trained psychologist accused of pushing his daughter-in-law to suicide. On the witness stand, he confesses to murder. The problem being that if he's found innocent of manslaughter, he can't be tried for murder for the same crime; double jeopardy. (He's convicted of man 1, and Adam Schiff points out that if he was guilty of murder, he just got himself "one hell of a plea deal.")
CI has raised to the level of an art form with the Handwave/Justification that causing Motive Rants is what Goren specializes in.
Criminal Intent has also subverted the rant on one occasion when a suspect is driven to confessing, but it turns out that she didn't really do it.
Also subverted in another episode (where the overbearing nature of her husband causes a woman to kill two her children in a failed mass-suicide attempt) where Goren successfully caused the husband to break into a motive rant, but it ends up being all for naught because he never really did anything illegal.
Subverted at first in the Grand Finale of The Fugitive, where the One-Armed Man, finally captured and interrogated by Lieutenant Gerard, clams up and demands to see his lawyer when Gerard cuts through his alibi. Things go differently when Kimble forces him to confess, but it's less of a rant than a feeble defense.
Mostly averted in Angel, where most revealed enemies tended to give a one liner before trying to kill him, or not have any idea who he was and just trying to kill him. Nevertheless Connor gave one near the end of season four. Somewhat notable for being delivered solely to someone in a Convenient Coma and being a despairing rant rather than a self-righteous justification. Jasmine got a shorter one, shortly before that.
The secret Big Bad of season two of Veronica Mars, Cassidy gave a particularly jarring one of these. In the last ten minutes or so he suddenly snapped into a pure Diabolical Mastermind mentality, despite this being completely at odds with his established character and his actual motive. Then, when he finished his speech and things went wrong, he reverted to his original personality. The worst part is that it was just about believable that he would do, well, some of things he did, with his established character, and if he had stayed in character instead of channeling a Bond villain it might not have seemed so unbelievable.
Subverted in an episode of Psych. After The Summation, the murderer simply said "I have nothing to say. Speak to my lawyer."
Hilarious subversion in Pushing Daisies when the killer delivers a crazed speech detailing his motivation — which the protagonists can't hear at all, because they're trapped in soundproof bags.
Generally, the show didn't do these; because it had a narrator to explain the motives, there was no need for the actual killers to do so.
Alias has a neat treatment of the trope in the season one episode "The Coming Darkness." Sloane muses to Jack how he's been having a pretty bad week (due in no small part to Sydney's and Jack's efforts), and reminisces at length about a time when he felt "a coming darkness". He mentions that before he and Jack even met, he had a "perfect moment"... and though the CIA hadn't yet betrayed him and the wife he hadn't even met yet had not yet been diagnosed with cancer, he felt what he called a "coming darkness". So, he sums up: whenever things go very badly, he just reminds himself he could see it coming all along. And then he coldly hisses that he wants one of the things vexing him dead before the weekend.
In one episode of Star Trek: Deep Space Nine, Dax (Ezri, not Jadzia) is chasing a serial killer who turns out to be a Vulcan. After catching up with him, she asks why he did it. In an aversion, he responds "Because logic demanded it.", the Vulcan version of "God made me do it." Although, when you think about it, this is an explanation — kinda.
Inverted in the episode "Duet"; a Cardassian identified as Gul Darheel, commander of Gallitep, one of the most horrific interment camps during the Cardassian occupation of Bajor, ranted at length about how he was a loyal Cardassian soldier and it was his patriotic duty and privilege to exterminate Bajorans. Toward the end of the episode Kira discovered that the prisoner was not Gul Darheel, but a file clerk at Gallitep, who was completely horrified by what his people did to the Bajorans and assumed the late Darheel's identity to force his people to own up to what Cardassia did to Bajor. In a Downer Ending, he's stabbed to death by a Bajoran just for being Cardassian after he's released.
In the musical It's A Bird, It's A Plane, It's Superman Dr. Abner Sedgwick explains his motive in songnote It's Revenge, by the way..
Subverted in Misfits when the villain makes quite a valiant attempt to explain/justify her actions, but Nathan is playing his music over her rant and keeps interrupting her so the audience hears very little of what she's saying. All we know for sure is that her crusade had something to do with being teased at school for being a virgin.
Parodied in That Mitchelland Webb Look when the detective manipulates a woman into doing "the evil voice" and eventually an entire Motive Rant that ends in her suicide. He says that it's better this way, as he didn't have any other evidence and not all courts accept "the evil voice". He also accidentally provokes someone else into giving one, identical in tone to the first, except about not flushing the toilet instead of murder.
Criminal Minds doesn't have a huge number of these because episodes often don't show the killer after they've been caught and quite frequently they end up getting killed rather than arrested, but "The Fox" and "Poison" both had pretty chilling ones. It was also subverted in another episode where the murderer himself said that he didn't know what made him kill.
Possibly Fridge Brilliance at work, as a key premise of profiling is that serial offenders are really acting out their inner demons and insecurities, whatever superficial rationale they might layer on top of that. Any Motive Rant most perps would be capable of articulating is only their self-justification, not their motive.
Assuming the profilers are doing their jobs, they'll have deduced the content of an offender's Motive Rant before they actually meet up with the perpetrator.
For example, in "Masterpiece" the killer turned himself in to police after kidnapping five people, saying they'll die if not found in a few hours. The team finds where they're being held and leave, except for Rossi, who continues interviewing the killer. At this point, the killer reveals that the location is a trap, and launches into a full-on motive rant, revealing that Rossi had arrested his brother (also a serial killer) and he'd wanted revenge. Cue Hotch calling to tell Rossi that the trap was right where he'd said it'd be, and all the victims are fine. Rossi'd guessed the trap, but intentionally triggered the motive rant to get the killer to admit to his other killings on tape.
Castle gives one of these for the killer in one episode, identifying his motives well enough that the killer gets caught up in the story and confirms it's exactly how he felt.
Castle alternates between this and just asking to see their lawyer.
Lately, it seems that asking for their lawyer is a sign that they didn't do it.
In Game of Thrones, Petyr 'Littlefinger' Baelish gives one for the ages with his "Chaos is a Ladder" rant. Even his fellow Magnificent Bastard, Varys, is highly disturbed by it.
Petyr Baelish: Do you know what the realm is? It's the thousand blades of Aegon's enemies, a story we agree to tell each other over and over, until we forget that it's a lie. Varys: But what do we have left, once we abandon the lie? Chaos? A gaping pit waiting to swallow us all. Petyr Baelish: Chaos isn't a pit. Chaos is a ladder. Many who try to climb it fail and never get to try again. The fall breaks them. And some, are given a chance to climb. They refuse, they cling to the realm or the gods or love. Illusions. Only the ladder is real. The climb is all there is.
Subverted in Bruce Springsteen's song "Nebraska"; right before being executed, Charles Starkweather acknowledges that people want to know why he became a killer, but all he offers as an explanation is, "I guess there's just a meanness in this world." This is artistic license, however, as the real Starkweather didn't say that.
This is very common whenever a wrestler undergoes a Face-Heel Turn. The next week after, they will often tell the fans why they did what they did to a face wrestler, whether it's being tired of living under their shadow, either because they are sick of the fans and the locker room not giving them respect, or simply because they can.
Famously subverted at the end of Shakespeare's Othello. After Iago is captured and Othello demands to know why he tricked him into killing his own wife (something all the readers would like to know as well):
Iago: Demand me nothing. What you know, you know. From this moment forward I never will speak word.
Early on in the play, Iago had ranted that Cassio was promoted ahead of him, despite Cassio being newer to the army and Iago having served faithfully for much of his life. The rant also reveals that Iago is racist, and this, combined with his anger at not being promoted, is what caused him to seek revenge on Othello. He did it in a way that allowed him to act on both his reasons for hating Othello: he set up Cassio as someone Othello couldn't trust, and targeted Othello's marriage to Desdemona because he — and many other characters in the play — objected to the idea of a black man marrying a white woman. So the subversion at the end is sort of a Double Subversion; the audience knows why Iago did what he did, but the characters don't.
Salarino: Why, I am sure, if he forfeit, thou wilt not take his flesh: what's that good for?
Shylock: To bait fish withal: if it will feed nothing else, it will feed my revenge. He hath disgraced me, and hindered me half a million; laughed at my losses, mocked at my gains, scorned my nation, thwarted my bargains, cooled my friends, heated mine enemies; and what's his reason? I am a Jew. Hath not a Jew eyes? Hath not a Jew hands, organs, dimensions, senses, affections, passions? Fed with the same food, hurt with the same weapons, subject to the same diseases, healed by the same means, warmed and cooled by the same winter and summer, as a Christian is? If you prick us, do we not bleed? If you tickle us, do we not laugh? If you poison us, do we not die? And if you wrong us, shall we not revenge? If we are like you in the rest, we will resemble you in that. If a Jew wrong a Christian, what is his humility? Revenge. If a Christian wrong a Jew, what should his sufferance be by Christian example? Why, revenge. The villainy you teach me, I will execute, and it shall go hard but I will better the instruction.
One great example comes from The Engineer in Amnesia: A Machine for Pigs. Combined with stellar voice acting, his speech is widely considered to be the best moment in the game, not to mention one of the most magnificent examples of this trope. (It's on the Quotes page if you want to see it.)
It seems like all of the witnesses in Phoenix Wright: Ace Attorney and its sequels do this at least once. Once Phoenix starts to unravel their testimonies, every witness goes nuts and starts raving about their motive and how perfect their plan was (or, if they happen to be very pompous or arrogant, they become very quiet and submissive). This even applies on a lesser scale to the witnesses who don't end up being the murderer, in which case they usually just freak out and tell the truth, rather than lying as they had until then. The most notable example is when Manfred von Karma bashes his head against a wall a good 20 times after being outed as a murderer. In fact, at one point Phoenix notices something is amiss when a witness doesn't go into a Motive Rant.
An exception is Case 1 of the fourth game, where Kristoph Gavin admits his crime without any sort of motive being explained. This is of course questioned by everyone else and is eventually revealed at the end of the game.
Big Boss: I can say one nice thing about the Cobras: they mostly had the decency not to spew out their life stories, before or after I fought them.
The Beauty and The Beast unit from Metal Gear Solid 4 also avoid this, due to its members being completely Ax-Crazy. "Luckily," Drebin is happy to do this on their behalf via Codec every time Snake defeats one of them.
The Boss also has a monlogue before the final duel with her, in which she explains everything she had given up for her country, and how pointless it had been rendered by the Cold War (although she doesn't rant so much as just get it all off of her chest). Of course, with hindsight, it turns out to have been detailing her motive in terms of remainingloyal to her country, in spite of everything she had lost. And the fact that her death would leave her reviled as a traitor.
Mass Effect has Saren explain, twice even, exactly why he's working with the Reapers.
Jin Kazama in Tekken 6. "What have the governments, religions, and people of this world accomplished?"
At the end of Rainbow Six: Vegas 2, Big BadGabriel Nowak goes into a long-winded rant to his former teacher, Bishop, about why he chose to turn traitor, facilitate terrorist mass murder in Las Vegas, and steal government information to sell to the highest bidder. It was basically a rant about how he got screwed over for promotion, even though it was his own damn fault. Egotistically gloating about how he was going to destroy everyone Bishop cared about, he failed to realize that while he was ranting, Bishop had his gun drawn. Though Bishop was patient enough to wait for the rant to end, the player soon got a chance to shoot him and end the whole thing.
Doesn't help that Gabriel Nowak had displayed a level of professional incompetence that should have barred him from even his parent (pre-Rainbow) unit.
In the penultimate mission of Splinter Cell: Chaos Theory, Douglas Shetland gives a pretty impressive rant on what drove him to fund terrorists and try to start World War III. He then tries to pull a "I Surrender, Suckers", and things go downhill...
At the end of Conviction, Tom Reed does the same, talking about how the President was going to pull funding from Third Echelon and go soft on terrorism.
Ganondorf was just jealous of Hyrule's wind in The Legend of Zelda: The Wind Waker. In a variant, though, there's he's not gloating. He's just — nostalgic? bitter? remorseful? detached? Take your pick.
Say what you will about Shepherd having crossed the Moral Event Horizon, but after his simple but passionate statements about the sacrifices he has had to make, you can no longer look at him using simple Black and White morality.
In The Godfather game, "Monk" Malone gives you one as you're hunting him down. Various important mobsters also give short ones if you manage to grab and interrogate them.
Tsukihime, when it seems Hisui's True Ending has been played out... Shiki confronts Kohaku and she reveals she was the mastermind behind the various events and deaths that occurred. Her motive was revenge, because that's what she thought a normal person would do.
Adachi gets one as the player travels his dungeon in Persona 4. At the very end, he's given a Shut Up, Hannibal! by the protagonists and called out for his senseless motives.
Terumi Yuuki gives one mostly when unveiling Mu-12, stating that he thinks the world are nothing but lies, the only truth out there is despair, and he sure as hell will show them by having Mu-12 destroy Master Unit Amaterasu.
In Dragon Quest VIII, Marcello gives one that doubles as a "Why You ALL Suck" Speech and New Era Speech. Here, he informs everyone gathered there of his intention to use his new position to create a new world order — one where your position is determined SOLELY by your strength and ability, rather than who your family is. He also makes no secret of the fact he considers most commoners to be mere sheep who won't exactly thrive under these conditions...
Oguma from Metal Slug 3D, a mad scentist with a very soft voice who spends one long cut scene explaining his evil plan.
Assassin's Creed: In all games in the series, once you assassinate a primary mission target, time freezes so you can listen to the victim's Final Words, which are, almost invariably, a long diatribe on why they did what they did and/or why you're a terrible person for killing them. In some cases you get the speech as part of the lead-in to the battle, in which case their Final Words are typically some form of plea for forgiveness or understanding.
After Terrence in KateModern: Precious Blood has been revealed as the murderer by a group of unarmed individuals in the middle of nowhere, he for some reason feels compelled to explain at great length the full extent of his crimes (much worse than the single murder he was accused of) on camera. In his defense, he later admits to having been "a bit off [his] face" at the time.
Melina: You know? I never really liked men. Do you know why? It's because they always WANT something. Did you know that? Well, obviously you do. Men constantly WANT. They want to hold you, touch you, kiss you. They want to make you THEIRS. But? I never really liked that you know. That's why, instead of letting them TAKE whatever they want? I decided to WANT and TAKE from them first!
The Simpsonsdid it. In "Sideshow Bob Roberts", when Lisa insinuates that Bob is too stupid to have rigged an election and claims Bob's Rush Limbaugh look-alike accomplice is the real brains of the operation, Bob flies into a rant about how he (and only he) had the brains to orchestrate everything, parodying the A Few Good Men quote above. He is then promptly taken to jail for "all that stuff [he] did" with unusual expediency for the Springfield police.
Practically every Scooby-Doo story ever written ends with one of these, once the villain's been unmasked. And of course, he would've gotten away with it too, if it weren't for You Meddling Kids.
Almost; usually, it's the kids who reveal the motive for him/her.
Scooby expy Clue Club does as well. Larry will break down how the crime was committed using physical clues and forensic evidence provided by Dotty before identifying the culprit.
Parodied in Kick Buttowski, while telling the class about something amazing he did, he quickly gets questions from the not so convinced teacher and Kendall, only to have the interrupted by Jackie who goes into the "You can't handle the truth" speech... only for everyone to tire of her ("Not this again...") and lower a sound-proof glass dome around her desk.
One of the most notable examples in western animation comes from The Last Unicorn when King Haggard (who is voiced by the legendary Christopher Lee) explains to Lady Amalthea, a unicorn transformed into a human, why he has captured all the other unicorns. Link
I like to watch them. They fill me with joy. The first time I felt it I thought I was going to die. I said to the Red Bull I must have them, I must have all of them, all there are! For nothing makes me happy but their shining and their grace. So the Red Bull caught them. Each time I see the unicorns, my unicorns, it is like that morning in the woods and I am truly young, in spite of myself!
The Rugrats episode "The Trial" has Angelica revealing that she did break Tommy's lamp after failing to pin it on Chuckie, Phil and/or Lil. It's a bit of Karmic Retribution as Angelica starts gloating that, even though she confessed, they couldn't do anything because they can't talk... forgetting that she can. And Didi and Betty heard the whole thing.
In season 2 episode 25 of Wakfu, Qilby the Traitor starts ranting after getting the upper hand in his fight with Yugo. He basically reveals himself to be a selfish nihilist who honestly believes he has the right to sacrifice entire worlds to fuel a tour of the cosmos to stave off boredom. He repeats the rant in episode 26 after losing the Eliacube when Shinonome turns against him, whining about the misery immortality brought him.
While not a criminal, Danish comedian Anders Matthesen wins an award for being a role model, and throws a Motive Rant in the direction of the secretary of education (Bertel Haarder), who accused him of being an Anti-Hero: "Bertel, blow me! I'm not a fucking anti-hero. What are you talking about? Anti-hero, I don't know what the fuck you're thinking? I've always said, which the people who listen to me and have voted for me can confirm, that I believe that you shouldn't do drugs, you shouldn't waste your own time or other people's time, that you don't do violence and that you always do your fucking best, which I think a real role model should be doing."