In an Alternate Universe version of the Edo period, Japan was occupied not by the usual Western fleets like you'd expect from normal history — but by a race of space aliens known as the Amanto, who brought with them super-futuristic technology (resulting in things like mopeds, TVs and robots being invented earlier then usual), a ban on swords and the fall of the samurai class as we know it. A resistance group set out and declared war on the Amanto to no avail, and the samurai were all but wiped from the map. Enter Gintoki Sakata, a former member of said resistance group; once an impressive swordsman, he dropped out because in the end, it really wasn't worth it to be fighting against a bunch of stupid foreigners in the first place.Nowadays, Gintoki makes his living as a self-appointed freelancer, taking on any job he can for cash to pay his rent, but that doesn't seem to happen very often when there's sweets and Shounen Jump to be had. Joining him in his exploits are samurai-in-training Shinpachi Shimura, who winds up taking the brunt of much of the series' abuse and leads a pop idol's fanclub; Kagura, a young alien girl who spends most of the time eating, beating someone up, or just generally being an idiot; and Sadaharu, Kagura's giant pet dog that gleefully chomps on everyone and anyone. A lot.Gintama is the sometimes-anachronistic brainchild of Hideaki Sorachi, who had originally intended to create a manga inspired by an NHK drama about the Shinsengumi. However, despite the historical connotations that the Edo period brings, it's a Gag Series in one of its most warped states, filled with Shout Outs to everything under the sun (even fellow Shonen Jump series such as Bleach and One Piece are not immune to lampooning), over-the-top humour, ridiculous puns, sight gags and a liberal dash of action to top it all off. Stories tend to emphasize no such thing as black and white and how that plays into the Japanese concept of honor.After the manga premiered in 2004, a one-episode OVA for JUMP Festa was produced; a Sunrise-produced TV series made its debut in April of 2006 and finished its run in March of 2010, after which Yorinuki Gintama-san (literally "The Very Best of Gintama") followed, which was essentially just reruns of old Gintama episodes remastered in HD with new opening and ending themes, eventually the reruns came to an end and in April 2011 Gintama was finally continued as Gintama' (Note the dash)... until thatended in March 2012... and returned with a new season on October 4... which later ended in March 2013 as well, apparently this time for real. It has been mentioned however, that should the second movie do well enough, then the higher-ups will likely take notice.An English translation of the manga was published by Viz but was cancelled after Volume 23 due to low sales. The anime is licensed by Sentai Filmworks, who have so far released the first season on 4 DVD sets, as well as the movie adaptation of the Benizakura arc on DVD and Blu-Ray. The DVD releases for the show is unfortunately sub-only, though the movie was released with an english dub, and according to The Other Wiki, Sentai Filmworks may or may not release more of the show depending on how well the movie does.Complete with its own Character page, Shout-Outs page, and Ho yay page where contributions are greatly encouraged and appreciated.
This show provides examples of:
Accidental Hero: Gintoki and Hattori save the town from an extremist Anti-Foreigner Faction trying to destroy the Terminal. They were actually fighting over a double-issue of Shonen Jump.
One of the 3Z Ginpachi Sensei omake has a funny one, in which Tomokazu Sugita tells about how he got a call from his mother after the Stand Inn arc was aired, telling him he really should work on his singing.
Episode 150 includes a frame-by-frame parody of a scene in Neon Genesis Evangelion. Hasegawa takes the place of Gendou Ikari, both of whom are voiced by Fumihiko Tachiki. He also, sometimes does some mannerisms as Gendou.
In episode 122, before he was revealed, the Eyecatch has his silhouette shaped like Kenpachi
Taken to the extreme in fight between Elizabeth (Tohru Furuya) and Dark Vader (voiced by Shuichi Ikeda), to resemble the fight between Amuro Ray and Char Aznable in Mobile Suit Gundam. The staff even made Elizabeth pilot the RX-78 Gundam.
Hijitaka says LET'S PARTY! in in his introduction as hosts in the Takamagahara host club. The difference is, instead of a horse, Hijikata uses Kondo as his Harley Gorillason!
Adaptation Expansion: Several of the stories in the anime are lengthened compared to their manga counterparts.
Beautiful All Along: Played with. In the Love Choris arc Gintoki uses all-out willpower to make Pinko look this way. Of course, the justification is that adults have to use their imagination to make their now-old-and-ugly partners look more attractive...
What started the hilarious harem arc, with Gintoki waking up in a love hotel next to... Otose.
Belly Mouth: One member of Shinpachi's fan club in an early episode is an Amanto that forms a mouth on its stomach and devours things when it gets excited.
Belligerent Sexual Tension: Sogo and Kagura mostly. Both instantly tease and provoke each other whenever they meet. He's also been getting some with Nobume too since the Baragaki Arc.
Big Damn Heroes: Gintoki gets to do this a lot (must be in the contract for a Shonen series' main protagonist). A candidate for his best one so far? Stabbing Jiraiya's hand while suddenly showing up from behind a tied-up Tsukuyo, then swatting him away.
Bifauxnen: Mutsu, who's flat chested, and talks and dresses like a man. Also Kyubei.
Bishounen: Okita is by Word of God the token bishounen. Katsura and Kamui also count, and one should certainly not forget about Honjo from Takamagahara host club. Shoyo could be considered too, after his face has been revealed.
Blade Run: Gintoki does it on Benizakura in his third fight against Nizo.
In episode 202, Kondo claims that eating Otae's omelet will allow him to forget everything bad that's happened. This is a call back to the Amnesia Arc a 150+ episodes ago where the exact thing happened to Kondo.
Bridal Carry: Gintoki carries Tsukuyo this way after freeing her from Jiraia's web, in the very ship-teasing Red Spider Arc.
Yamazaki falls victim to lots of punishment, especially from Hijikata.
Kondo, the butt gorilla, keeps getting beating after beating from Otae, in addition to whatever Matsudaira or karma has in store for him.
Zenzo takes plenty of abuse from Ayame, most of which literally aimed towards his butt—on top of his hemorrhoids—making him another literal instance of a butt monkey.
Prince Hata; you know he's going to get abused the moment you see him. Nothing good ever happens to him.
Shinpachi is the butt monkey for the Yorozuya trio, often having to put up with his companions' insults and laziness/retard-ness/plain old idiocy. The crossover episode in  also had him being rejected by Himeko. However, he's also the Straight Man (Tsukkomi) or the mother of the crew, so he seems to be able to hold his own by yelling at Gintoki and Kagura whenever they do or say something inappropriate. Which is often.
Cerebus Rollercoaster: Most of the time it's comedy and gag, with the occasional heart-warming or tear-jerking episode. Then it gets very serious over the course of an arc before going right back to comedy and gag until the next serious arc comes around a while later.
Chekhov's Gunman: Remember minor character Ana Ketsuno being married (who would) WAAAAAAAY back then? 150+ chapters later, not only does she gain an important role in the Onmyoji arc, her marriage becomes a major plot point in the arc.
Kagura befriends Princess Soyo, the Shogun's little sister, in chapter 23, from which point onwards she doesn't really appear again until 364 chapters later in the Courtesan of a Nation arc, where Soyo returns with their friendship being brought up again. It's what allows the Yorozuya and Tsukuyo to enter the Shogun's castle.
Chekhov's Gun: One of Katsuo's minions mentions very early on that Jirocho used to be in love with Otose. This becomes a very important plot point much later in the Four Devas Arc.
Christmas Episode: Two episodes of characters attempting to prove that they're the real Santa to achieve their own goals. The real Santa does show up in the series, but not in this arc.
Creator Cameo: Sorachi appears in both anime and manga in the form of a gorilla, a humanoid Half-Dressed Cartoon Animal sporting a yellow t-shirt, he still is a manga-ka in this caricature of him and for some reason Gorilla Sorachi is always seen in trouble, lacking ideas for the manga he is working on.
Depraved Dentist: The dentist in episode 175 is this, complete with blood-spattered operating room, chairs with steel restraints and a chainsaw.
Diet Episode: One episode features most of the major female characters having become obese within the same time period and enrolling into a fat camp. They all go back to normal at the end of the episode after eating laxitive-laced chips.
Elite Mooks: Kada's Shinra soldiers and Oboro's Naraku certainly prove to be tougher challenges than the regular Mooks faced by the cast, though they still die by the droves. Interestingly, both groups are essentially ninjas in all but name.
Enemy Mine: Gintoki and Jirocho team up with each other at the end of the Four Devas Arc to take on Kada and her Elite Mooks.
Epic Fail: Oh man, too many times to count the main characters have tried to avoid making problems in situations only to make it a lot worse. The most prominent example probably has to be the Yorozuya's every encounter with the Shogun, where everything they do goes wrong in the worst possible way.
The Faceless: Hatsu, Hasegawa Taizo's wife. Strange in that she isn't an important character at all.
Gintoki, Katsura, and Takasugi's sensei, Shouyou, at least until the Courtesan of a Nation Arc, where his face is finally shown.
Fake Memories: In the Kintama Arc, Kintoki (the evil robot counterpart of Gintoki) brainwashed almost ALL of Kabukicho and Yoshiwara with soundwaves to forget a certain main character named Gintoki Sakata. He replaces all mention and image of the silver-perm haired with his own straight perm and gold identity... to become the series' protagonist! Except that he couldn't replace the memories of the man himself, as well of those of Sadaharu and Tama, because the wave didn’t work on animals or other robots.
Fate Worse Than Death: An interesting contrast. Many antagonists in the more serious arcs pass away peacefully through the power of Flashback (ex. Hosen, Jiraia, Ito). On the other hand we have Kada who survives only to completely crack under incarceration.
Females Are More Innocent: Invoked. Of all the female antagonists, the only recurring one is Matako who's in it out of love for her boss. Out of the rest, Kada got imprisoned, not killed like most other male Arc Villains; Pirakogot away scot-free and probably won't come back; and Catherine joined the Yorozuya's side early in the series. Though where Nobume stands on the matter remains to be seen.
Filler: There's actually very little anime-original filler, but they do occasionally pop up. The most commonly seen fillers are those involving the anime supposedly ending.
Felony Misdemeanor: Seriously, Hijikata, chill. Shonen manga is not worth committing seppuku over.
Fixing The Game: Gintama played with this trope by having a man gifted with the ability to see the flow of luck. Though as it turned out he lost that ability a few years back and has been cheating at games since then.
The Four Gods / Four Is Death: The Four Heavenly Emperors of Kabukicho which rule over the district and shouldn't be confused Four Heavenly Emperors of the Yagyu Clan. The latter would probably be more fearsome if they weren't named after the main four romantic interests of Strawberry 100%.
Fourth Wall Mail Slot: Usually run by Ginpachi-sensei, and answered in character with no regard for the fourth wall.
Notably someone asked at the end of episode 146 why Kagura's brother was animated as having black hair prior to his first proper appearance in the anime. Had they perhaps imagined it? Gin answers that they didn't imagine it.
Freaky Friday: Happens with Gintoki and Sadaharu at one point in the anime with no explanation. Later on it also happens with Gintoki and Hijikata after they got hit simultaneously by a truck.
Funbag Airbag: Tsukuyo wants to prove to Gintoki that she's abandoned her identity as a woman by letting him touch her breasts. Gintoki would have none of it EXCEPT he saw a spider. He then falls headfirst on to Tsukuyo's breasts (and, for the hell of it, gropes them anyways), who unfortunately does not want it and does a frickin' SUPLEX on Gintoki, crashing him through the door of the druggies hideout.
Gainax Ending: Several fake ones, actually. The premise of episode 150 was that the show was abruptly ending due to lack of funds, so they threw together a final episode. Several versions of this "final episode" are shown. All of them start with a showdown between Gintoki and Takasugi and spiral downwards from there.
In one ending, Gintoki pitches a baseball at Fenway Park, Elizabeth becomes a robot and Shinpachi dies.
Gender Bender: As punishment for blurring gender roles, the followers of Dekobokko swap the gender of the residents of Kabukicho and a number of people who were coincidentally in Kabukicho at the same time, such as Kyuubei, Tsukuyo, Sa-Chan and the Shinsengumi. The only ones unaffected were Shinpachi (His glasses only turned pink) and Tae (Who was outside of Kabukicho when it happened).
Genre-Busting: The series as a whole is a "sci-fi human drama historical comedy". According to Word of God, every individual chapter has its own genre.
Gosh Hornet: Subverted in chapter 269 (ep 185 anime), when Gin is hired to exterminate a beehive... filled with alien half-man half-bee gangsters. He and Kagura accidentally destroy three hives within the chapter.
The Greatest Story Never Told: In the second segment of episode 21, Gintoki essentially saves the world while looking for an electric fan. Even though the episode's Damsel in Distressautographed the fan, Shinpachi and Kagura still refused to believe him.
Great Offscreen War: The Joi War is often referenced during the course of the series and many notable characters took part in it, but only few flashbacks of the war are shown at best.
Groin Attack: Gin's tama even fell off at one point. And then got individual names. And were then slammed repeatedly into each other. Hard.
Also often evaporated or transformed into some random tool. Lampshaded in the  Crossover Special. Since his tama were named after Bossun/Yusuke and his Rival and twin brother Sasuke.
Also lampshaded when during the arc inside Tama's body, it even gets pixelated! "Why is all the enemy fire concentrated there!?!"
Hachiko: A story that Gintoki hears on the radio is based on Hachiko, though the dog's owner isn't dead. Neither is the dog.
Hachimaki: Part of the required uniform for Otsuu's fanclub.
She was meant to be a parody of The Ring... at first.
Healing Factor: Anyone from the Yato Clan has this. To illustrate, Kagura is able to recover from gunshot wounds over one night.
Heir to the Dojo: Subverted, in that while Shinpachi and Otae both inherited their dojo after their father's death, they're the farthest thing from rich you can think of (the dojo nearly becomes repossessed in one episode) and nobody really studies there, either. They finally start it up again in the Beam Saber Arc and Shinpachi is shown to still be teaching students in the Gender Bender Arc.
Heroic Sacrifice: Subverted in episode 47, in which the Yorozuya are convinced Hedoro came to invade the earth:
Gin (grabbing his bokuto): I'll keep him busy. You guys run in the meantime. [...] (lunging at Hedoro) Hedorooo! I'll never hand the Earth to you!!
Shinpachi (running with Kagura): Gin-san, I'm so sorry! I'm just a wuss! All I think about is saving my ass by sacrificing yours-
(later) Gin (running behind) : NOOOOOOOO!! (slaps Shinpachi and Kagura out of the way)
Shinpachi: Gin-san? Weren't... Weren't you sacrificing your life to save the Earth?!
Gin: My life comes before the Earth!!
Played straight with Tama at the end of her arc, though they manage to rebuild her.
Hidden Villain: While most of the arc is focused on Jirocho and Pirako, the real villain of the Four Devas Arc is Kada, who is also revealed to lead the 4th Division of the Harusame Pirates!
The trope is parodied in one chapter when Katsura enlists the Yorozuya (plus Sacchan) to save Elizabeth, and they have to become ninja to do so. Sacchan demands that everyone wear different, highly visible costumes because she can't tell them apart otherwise. Gin ends up in a white ninja outfit, Kagura in red, Katsura in yellow, and Shinpachi in a cow print. Their attempts to use ninja camouflage fail about as miserably as one would expect.
Hikikomori: Your Brother is a Hikikomori! "Quit being a burden and go do volunteer work or something!"
Historical In-Joke: Tons - most of the main characters are based on real people, and thus a lot of the humour comes from what alleged heroes are generally like when they're not actively being heroic. Oh, and the thing about firing a laser cannon at the capital? Happened in real life, albeit with a regular cannon. Even the Customer of the Week is often a comedic version of a historical figure.
Episodes 233 and 234 feature the Renho (Elizabeth's race)'s trump card for invading Earth — the Gunsam. One of them even gets hijacked in classic Gundam fashion. Lampshaded by the characters, who note that they would have been sued if the show hadn't been animated by Sunrise.
"So, in the end, you played with the Mega Drive, too?"
La Résistance: The Anti-Foreigner Faction during the Joi War. Katsura and his faction try to be one in the present, but they're hilariously inept.
Lethal Chef: Otae. Shinpachi even suggests that his bad eyesight is from eating too much of her cooking.
...and it's been shown to cause amnesia. Lethal, indeed.
Somehow she was able to burn sushi in HER HAND.
Light Feminine and Dark Feminine: The series offer quite a good spectrum of this. Kagura, Otae, Tama, Otose, Princess Soyo and Hinowa are the Light Feminine whereas Tsukuyo, Kada,Kyuubei, Mutsu and Matako embody the Dark Feminine. Straddling the line are Sacchan, Catherine and Pirako.
Men Are the Expendable Gender: Partially averted. The Yoshiwara Arc shows females being killed and battled casually due to the presence of an Amazon Brigade. But other than that, it is fairly rare to see a woman die, even in serious arcs.
Miniature Senior Citizens: Kyubei's grandfather Binbokusai, who happens to be a great swordsman despite his height, as well as Maizo and Suzuran. Not to mention Gintoki and almost everyone from the main cast when they got aged in the Ryugujo Arc.
Mood Whiplash: Played very straight. You WILL find yourself crying or at least on the verge of tears just watching a few of those episodes.
Or alternatively you will find yourself bawling your eyes out only to watch the ending and be filled with the inexplicable urge to throttle Sunrise and Sorachi for trolling you all while laughing your guts out because the whiplash was so harsh it became hilarious.
Mook-Face Turn: Tsukuyo manages to convince her own Hyakka to rebel against Hosen with her after having earlier defected herself to help the Yorozuya reunite Seita with Hinowa.
The Movie: Two movies so far. The first is a movie adaptation of the fan-favorite Benizakura Arc with the backing of Warner Bros. . It then got a second movie in Summer 2013 written by Sorachi himself.
Mr. Fanservice: Many of the male characters. Even with all of their... quirks. Special note goes to Gin - one year he has ranked 1 in a number of polls, including an anime husband and valentines poll.
This is followed by a montage(with a nice melody) of Kagura strolling around the streets happily, the montage is repeated with slightly heavy rain with more rock added into the music. She still went out with the umbrella even when there's a typhoon rampaging outside.
Never Trust a Trailer: The in-magazine post chapter previews attracted some criticism in Japan because they were always made in the early stages of writing the chapter in question, meaning that the preview and the actual story always ended up completely different to the point of being funny. It was quite common to have a wacky-sounding preview like "Gin enters a marathon!" only for next week's story to be deadly serious. Very likely intentional, this being Gintama after all.
New Powers as the Plot Demands: Parodied. The main trio is suddenly brought into another dimension by a sage to learn new, secret techniques, but all of them believe that they're strong enough already and actively avoid learning anything.
The most known example is the Popularity Poll Arc. It starts with the announcement of the results of a fan poll to determine the most popular characters that people voted in the Weekly Shounen Jump magazine in 2009. The arc (spanning four chapters and three episodes) proper is entirely based on the results of this poll, with several characters depressed over having finished lower than expected while others gloat over their good showings. Also, every time anyone appears onscreen and on-panel, a number floats above their head reminding the viewer what place they got. And then shenanigans happen from Otae CLIMBING OUT OF THE FRAME announcing she would kill the character who placed ahead of her (being the series creator), and people FIGHTING over their popularity, to form alliances with others to claim their places, etc.
The lack of a fourth wall somehow works both ways—the author once told an anecdote that when a rumour spread about Chinese women coming and going from his apartment, he (in a sleep-deprived state) initially wondered if they were talking about Kagura, before reminding himself that she isn't real.
And the characters (mostly Shinpachi) often wonder if the constant parodies, references and such would serve a proper sue for them.
Omniscient Council of Vagueness: The Tendoshu, a council of twelve Amanto who are the true power behind the Bakufu. While introduced early on and are important to the backstory of the series, they've only rarely appeared and don't really become important to the story again until the Courtesan of a Nation Arc.
Only Six Faces: It's noted and lampshaded early on, but it's not actually used.
Onmyodo: The Shirino and Ketsuno clans are both composed entirely of Onmyoji.
She originally had six wings, but they were burnt off by her kotatsu.
Overly-Long Gag: Katsura's tales that have nothing to do with the plot of the chapter taking place. One example is in episode 110, Katsura was led into counting sheeps so he could fall asleep. On the 13th sheep, he began fantasizing an elaborate and sad tale in High School AU style for this 13th sheep for a full 4 minutes!
People mistaking Shinpachi's glasses for him.
Chapter 314, Kyubei gives a long name to the monkey she was taking care of. Its name is Jugem-Jugem Poop-Throwing Machine Shin-chan's Day Before Yesterday Underwear Shinpachi's Life Balmunk Fezarion Isaac Schneider One Thirds Pure Feeling Two Thirds Worried-Over-a-Hangnail Feeling Though Betrayal Knows My Name I Know The Unknown, The Cuttlefish Tastes Kind Of Different Than It Did Last Time Because It Was Caught Near The Pond And Served With Oil From A Hoofed Mammal, pepepepepepepepepepepep Bichiguso-maru.
The cursed Blu-Ray player and her kotatsu story. It goes from a gag where she's worried if she has turned her kotatsu off to a cliche domestic abuse story. Don't ask me how.
The Hard Boiled episode beats a dead horse with it's own leg.
Parasol of Pain: The weapon of choice for the Yato clan; features bulletproof fabric (though apparently not melee-proof), integrated machinegun and, of course, sun protection. Thanks to the Yato's strength, these have a huge size variety: Kagura's is normal in size, but Hosen's is about the size of a car!
Parody Names: Unfortunately this is lost in translation, but this "Shinsengumi" is spelled with different characters from the real one. ("True selection corps" rather than "Newly selected corps".) More recognisably, many characters have the names of their real-life counterparts with a single kanji changed: e.g. Kondou Isao instead of Isami, Sakata Gintoki instead of Kintoki, Katsura Kotarou instead of Kogorou.
Perverse Sexual Lust: In-universe, Shinpachi starts a fistfight against someonenote Toshi, Hijikata's Otaku ego who tells him that loving an Idol Singer is about as realistic as this trope.
Pixellation: Used frequently to the point of ridiculousness. Pixellated vomit tetris anyone?
Platonic Prostitution: Gintoki is maneuvered into this situation with Tsukuyo at the end of the Red Spider Arc after being promised free drinks. Tsukuyo assumes that she's supposed to sleep with him in gratitude for him saving Yoshiwara, but Gintoki is appalled at the suggestion and instead gets her to sit down and drink with him. It would have been a nice, friendly evening after that had it not been discovered that Tsukuyo has an extremely low tolerance for alcohol.
Retro Gaming: Nearly everyone makes references to Dragon Quest and other famous game franchises throughout the series. Katsura in particular is a big fan of the Mega Drive and Famicon. Goes the distance in episode 167 where Tama gets sick and transforms into an 8-bit sprite, complete with Dragon Quest style dialogue windows, earning EXP from going shopping and an inventory full of standard Dragon Quest items like medical herbs and a cypress stick. Then again in 168, where the opening segment is a brief 8-bit game sequence starring Tama. The rest of the story arc is one big Dragon Quest parody.
Riding into the Sunset: Happens a lot at the end of an episode/arc to highlight the heartwarming aspect. Occasionally subverted for Gintama's trademark trolling.
Running Gag: Plenty. There tends to be at least one per character.
Schizo Tech: Robots, laser cannons, and video games exist in what is otherwise Meiji-era Japan, leading to things like samurai fighting on spaceships, and bright Zeerusty towers literally next door to traditional Japanese houses. And even the robots come in "steam-powered tin can" and "ridiculously human" flavours, with nothing in between.
Self-Deprecation / Biting-the-Hand Humor: Everything about JUMP, especially the immaturity of its comics, is constantly mocked. Gin is treated as a loser for reading it, all glimpses we see of comics within it are scribble-quality, and any member of the Shinsengumi who reads it must commit seppuku to atone.
The author's commentaries in the compiled volumes are pretty much nothing but this, like a "how to draw" column that highlights his inability to draw more than one incredibly ordinary face, or saying that the unique aesthetic of the comic comes from the fact that it's "really poorly drawn". He also complains about his editor at every opportunity and at one point described working on a deadline as "walking a tightrope made of toilet paper across the Grand Canyon, and there's a monkey that looks like my editor peeing on the toilet paper".
The anime isn't better, they constantly talk about their poor rankings, No Budget and the production team.
Self-Serving Memory: Katsura and Hasegawa requires to this especially in the Zombrows mini-arc. Even lampshaded by Shinpachi pointing this in the manga panels.
Self-Parody/[Trope Name]: In one chapter, Gin gets sick and Kagura decides to take over his identity until he gets better. The result is a highly exaggerated parody of the story's usual formula:
Shinpachi: No, it's too soon for the cool, heartwarming speech! We're only two pages in!
Gintaman. The levity of the characters is almost entirely removed leaving something so gruff that's it'a hard to take seriously. To say nothing of how Gintaman was influenced by Gintoki lecturing the author of the manga (a gorilla) on comedy and how to write a popular shounen manga.
Serial Escalation: This series attempts to find out just HOW FAR they can make parodies out of any series. Episode 150 takes this to the extremes though with the infamous Neon Genesis Evangelion episode 26 where they literally copied almost frame to frame with Shinji and Shinpachi. To drive the point home, Hasegawa is in the same position as where Gendo was and both have the same seiyuu. Here's the video itself with a comparison.
Seppuku: Breaking any of the Shinsengumi's many rules is punishable by seppuku, which Hijikata ruthlessly enforces.
Shaggy Dog Story: Gin and Zenzo have an epic battle for the last copy of that week's JUMP...only to realise that it's actually a different issue.
The Shinsengumi: With bazookas. Chances are your impressions of the Shinsengumi will never be the same again.
Gintoki and Tsukuyo have had ongoing Ship Tease since Tsukuyo's introduction, most prominently in the Red Spider Arc which heavily teased the pairing. It even had Gintoki carrying Tsukuyo in his arms after freeing her from Jiraia's web.
Prior to Tsukuyo's introduction, Gintoki had ongoing Ship Tease with Tae. The umbrella scene in the Benizakura Arc is probably the most notable of these.
Tae and Kyubei are heavily teased in Gintama's openings and endings, which usually amp up the yuri subtext between the two quite a bit.
Shoo Out the Clowns: Throughout the gag episodes, even the main characters seem to have the default reaction to flee before danger, leaving their comrades behind (often followed by a Taking You with Me moment). However, when there's a serious arc going on, that behaviour is forgotten and they strive to protect one another in battle.
Smoking Is Cool: Definitely Hijikata. Also Tsukuyo, Otose, Hasegawa, Matsudaira, Jirocho and Takasugi.
The Smurfette Principle: Averted. While the Yoroyuza Gin is a classic Two Guys and a Girl dynamic, there are plenty of supporting female characters who actively participate in the different story arcs of the series.
Spoiler Opening: Spoiler ending more like it, but why is Kyubei the only one wearing a Sarashi in the seventh ending(Where all of the guys are featured shirtless)?
Spoof Aesop: This goes hand in hand with Idiosyncratic Episode Naming; many episodes are named such things as "When you're tired, eat something sour!" or "A life without gambling is like sushi without wasabi."
Strawberry Shorthand: "Listen up! Let's say you drink too much strawberry milk, and have to use the bathroom in the middle of the night. But it's cold outside your bed. You don't want to get up, but the urge to urinate is just too strong! You make up your mind to go! You run to the bathroom, stand in front of the toilet, and let loose! You think that all your life has led to this moment! But then you realize! It isn't the bathroom! You're still in bed! That feeling of lukewarm wetness spreads like wild fire! But you don't stop! You can't stop! That's what I'm talking about! That's the truth of the strawberry milk! DO YOU GET IT!?"
Just don't let Sadaharu eat it combined with milk. Just don't.
Gintoki: Well, it's something like this: He fights with his rival and wins. (writes one arrow from Yamcha to Tien) Then become friends without knowing it. (writes another arrow from Tien to Piccolo) And a new rival appears, and he fights and wins again. (writes another arrow from Piccolo to Vegeta) And made a new friend... Repeating this and dragging it on is the standard JUMP formula. (Circles all the characters except Yamcha)
Konoshi: Oi! One persion is missing! Namcha?! Is that Namcha?!
Gintoki: Well, that's what the rival part is all about. (crosses Yamcha out)
Konoshi: Oi! Let him in! Let Namcha join in the JUMP system!
Gintoki: The next thing is... Let's talk about the comedy part. (kicks the board down, directly where Yamcha was)
This may be an Affectionate Parody, as the creator was sent a long letter from a fan saying though Namcha isn't strong physically, he is still a strong character, as he strives to do what's right even though he isn't as powerful as the others. Sorachi's response? "I agree."
When Gintama came back in episode 253, and Gintoki was upset at how it began, he said "Last time I saw a first episode so bad, Gintama was back in six months!"
This Is Reality: Probably the only time anyone's attempted to acknowledge the fourth wall (and it's made of balsa wood). In episode 169, the Yorozuya are attempting to cure Tama's illness. Because she's so obsessed with Dragon Quest, the arc is one big parody of the franchise, and at one point Shinpachi has to remind everyone that it's not really a game and they can't rely on standard conventions, such as save points, to get them through it.
Throw It In: The initial title of Yorozuya Gin-san was rejected by the editor, and another one was needed. Expecting that his other ideas would be shot down too, the author decided to play a little joke and submitted a random title his dad had made up: Gintama.
The Shinsengumi is now an empire led by (Ba)Ka iser Sougo 'Sadistic' Okita III, the Demon Vice-Captain title is now held by Yamazaki, and Hijikata is a living embodiment of Good Is Dumb, but not really. By the way, they want to conquer Edo. Yeah.
Training from Hell: Parodied to hell and back in chapter 229 (or episode 147, if you're watching the anime) through total destruction of the fourth wall. "Go train in another manga, I've heard of some good ones."
Traumatic Haircut: Katsura got his hair cut short after being supposedly killed in the Benizakura Arc. It grows back pretty quickly.
Trolling Creator: Sorachi is known as the greatest troll on the other side of Japan. There's even a special idiom for him, "Gorilla is playing with reader's crotch again."
True Companions: The Shinsengumi. Also, hurting Gintoki's friends can trigger Gintoki's change from a seemingly useless bum to the white demon.
Underground City: Yoshiwara is an underground Red Light District with its own laws seperate from the Bakufu. It was originally an underground shipyard where the Bakufu built its ships, but Yoshiwara and its residents were moved down there after its original destruction during the Joi Aar.
Unstoppable Rage: Kagura, under the influence of her baser instincts, when Abuto tries to kill Shinpachi.
Vitriolic Best Buds: Gintoki and Katsura. Also, Hijikata and Okita. Seimei and Doman seem to have turned into this by the end of their arc.
Weaksauce Weakness: The Yato Clan is one of the strongest species in universe, yet rays of sunlight tend to not treat them kindly. Hosen dried up after being suddenly exposed to sun, since he had been living under the ground for many years. Kagura in comparison merely gets weaker and dizzy if being outside without an umbrella, so they're probably generally adaptive.
What Did I Do Last Night?: Invoked with Sa-chan's first appearance, where she had fallen through Gintoki's roof and slept on top of him. Gintoki was drunk the day before and can't remember anything, so she uses that to her advantage to hide from her enemies. It's also the premise that starts off the Scandal Arc, with Gintoki getting absolutely wasted and sleeping with Otose, Tae, Kyuubei, Sa-chan, Tsukuyo and Hasegawa. It's subverted when it turns out to all have been a prank to get him to stop drinking, then double-subverted when it's revealed that Hasegawa was not in on it. Gintoki promptly heads to a bar to get drunk enough to forget he just learned that.
Wholesome Crossdresser: Gintoki Paako and Katsura Zurako anyone? Averted with Mademoiselle Saigou and her girls. They're very wholesome, just totally unconvincing.
Just name it, and, chances are, someone in Gintama's either done it or alluded to it. From Gintoki and Umibozu peeing on a dead wormlike alien (You Know What Happens if You Pee on a Worm) to Hasegawa wetting his pants and wearing a diaper to Hijikata zipping his pants and snagging the zipper on his private parts, a surprising amount of vulgar stuff happens. And of course, one has to mention Yoshiwara, the courtesan safe haven that even lets a kid run a toy store. In the Onmyoji Arc, a battle was literally fought with Gin's... tama (balls). The two fighters even gave them individual names. That last one was more of a Shout-Out to SKET Dance, due to the names they gave them.
Xanatos Gambit: Played for laughs of course since this is Gintama. The whole Popularity Poll Arc? All planned by YAMAZAKI!. He wasn't happy with his ranking so he started a war to get all the characters to reduce each other's ranking. Seeing as he wasn't the only one unhappy with his ranking, they almost did it without his help. The outcome of said war would help him either way
You Shall Not Pass: Parodied in the first chapter. Gin lets them pass after a single page (And he survives!). Played more straight when Tsukuyo holds off her Hyakka to give the Yorozuya free reins to find Seita and reunite him with Hinowa.
Zeerust: A lot of the Amanto technology is like this.
Zettai Ryouiki: Tsu Terakado. Seems to be the standard fashion for teenage girls in Edo.
Kagura also wore them in the fourth ending, though it's relatively hard to spot. Her outfit in Yoshiwara also featured this.
The members of the Hyakka also wear these, usually fishnets.
Zombrow Apocalypse: Parodied in one episode where a special kind of virus strikes Edo, making those who are affected act like zombies... with the interests of useless old men who like to lay around all day and do nothing but play pachinko note a parody of Kochikame's protagonist Kankichi Ryotsu. Katsura immediately starts calling them 'zombrows' due to Genre Savviness and the unibrows they immediately sprout upon infection. It spreads quickly and soon only a handful of people are left. The situation looks hopeless, but because Gin already acts like a useless old man the virus passes him over and he manages to get everyone back to normal.