These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: Unlike most villains, Kintoki Sakata poses almost no challenge to Gintoki alone and their fight lasts for less than ten pages.
Asexual: There are a few fans insist that Gintoki is asexual. However, he's been shown spying on women in the shower, in the pool and on the beach. He also has a big crush on Ana Ketsuno and tried to hit on her once, but she was already married by then. He was also quite excited at the prospect of sleeping with the legendary courtesan Suzuran before he learned how old she was. On the other hand he resists most sexual and romantic advances from women and is comfortable in his bachelorhood, which may have something to do with how the women around him are either violent or obsessive when it comes to him. He has also bent Hasegawa over while drunk, even if both of them would prefer to pretend it didn't happen.
Base Breaker: Tsukuyo is one in Japan due to being a relative newcomer to the regular cast. She's still popular enough to rank 10th and 11th on the character polls, but she is also hated by some fans who see her as either a Spotlight-Stealing Squad or a threat to rivalling ships involving Gintoki, sometimes even both. She doesn't really count as one in the English-speaking fandom though, as she mostly remains a fan favorite there.
Crack Pairing: A series with this many characters who regularly interact with each other is bound to be rife in pairings, but the Japanese fandom really likes to get creative by shipping Sakamoto and Takasugi (who very rarely show) with the likes of Kondo and Hijikata (whom they've barely interacted with), as well as with each other (they were old comrades but they've only interacted with each other in a so far unanimated manga chapter). There were also doujin artists who published the Gintoki and Hasegawa pairing long before episode 239. Shinpachi has also been paired up with Sakamoto, Takasugi, and various unexpected Shinsengumi members for some reason or another. Other odd pairings include: Hijikata/Katsura and Elizabeth/Gintoki.
Kamui isn't even the main villain like Takasugi is and has only had two appearances in the actual story so far, yet despite this he managed to rank 7th in his first popularity poll and to the surprise of many later on jumped up to 3rd in his next poll.
Of the notable Shinsengumi members, Yamazaki is probably the least important and the most plain, yet despite or perhaps because of this he remains pretty popular, having managed to consistently rank in the top ten on the popularity polls.
Tsukuyo was one initially, having only appeared in the Yoshiwara Arc by the time the votes for the second popularity poll were being submitted, managing to rank 10th on said poll, making her the second most popular female character behind Kagura. However, her role has since expanded, to the point where she got her own arc right before the results of the poll was released. She has also become something of a Base Breaker to the Japanese fans.
Evil Is Sexy: Takasugi, Bansai and Kamui for the female fans.
Fan-Preferred Couple: Gintama has so far no Official Couples, and the chances of there being any are slim, but this has not daunted the shippers in any way. Okita/Kagura, due to the Foe Yay and Belligerent Sexual Tension between them, are ardently shipped together. A close second would be Gintoki/Tsukuyo (Though in Japan, it competes with Gintoki/Tae), especially after the Ship Teasy Red Spider Arc. Yaoi couples such as Gintoki/Hijikata and Hijikata/Okita are also hugely popular due to a large part of the fanbase consisting of Yaoi Fangirls. In fact Gintoki/Hijikata could probably be considered the most popular pairing in the fandom. The Yuri pairing would be Otae/Kyuubei.
Gintoki and Hijikata's rivalry throughout the series is often seen in this light, which has helped make them probably the most popular Gintama ship, particularly in Japan. The anime adding filler episodes with more Foe Yay probably also helped. The ship actually got lampshaded in Episode 92 with Gintoki holding a mock manga cover with them in a... erm, suggestive pose.
Kamui got just a little too excited at watching Gintoki fight Hosen. Cue Kamui's unhealthy interest in him. Umibozu even said Yoshiwara doesn't interest Kamui, he only became its ruler solely to prevent anyone from getting close to Gintoki, who he's staked his claim on as future prey.
Okita and Kagura have this in spades, so much so that whenever the two interact, it's almost always some kind of Belligerent Sexual Tension.
Nizo and Katsura, with Nizo cutting his hair off and caressing it against his face, talking about how it was soft like a woman's. If he meant to piss off Gintoki, it worked.
The Stand arc parodying JoJo's Bizarre Adventure becomes this since Gintoki shares a voice actor with Joseph Joestar, the main character for the second part of the series and who later on wields a Stand himself.
Another example with Sugita. In 2013, there was a manga chapter where Gintoki told stories involving Phoenix Ikki from Saint Seiya. When Ikki debuted in the spinoff Saint Seiya Omega the same year, he was voiced by none other than Sugita.
In episode 75, where Prince Hata dubbed as Takasugi much to Shinpachi's chagrin while Gintoki and Kagura made fun of it. Guess who took the role as Takasugi in Urakata Hakuōki this time.
Remember Shogun became a humanboard in the Winter Vacation Arc, It becomes this when Taiga Kagami brought one of the freshmen in basketball to become a human surf board just to get the Iberian Pork Sandwich right before the epic 'THIS IS A JAPANESE LUNCH TIME RUSH!' line at Kuroko's Basketball.
Well if it isn't enough, Zura... I mean Katsura ride TWO Mobile Suits (One Zaku in Jump Festa and a pixelled Original Gundam in Season 5) in this anime. Remember that he was voiced as Athrun Zala of Gundam Seed and its sequel, Gundam Seed Destiny who rode Justice Gundam in these 2 series
Idiot Plot: Arguably, anything that doesn't count as a serious arc has shades of this.
Memetic Loser: In more serious discussions Takasugi is spoken of as the dangerous Big Bad of the series he is. In less serious discussion however, the very same people will make fun of him for either his height or his constant rambling about destroying the world. The one-arc joke about his love of Yakult is also turned up to the level of obsession reminescent of other characters' Trademark Favorite Food.
Memetic Mutation: The "strawberry milk speech" and "evil grin" pictures are recognizable even to people who have never heard of the series.
Nightmare Fuel: Despite Gintama is a gag manga and anime, it doesn't stop to have some nightmarish moments, specially in serious arcs:
Chapter 13 shows Gintoki nigthmare about his past : while he was trying to rescue a friend on a mountain of corpses!, that corpses said that he cant protect anyone and it end that the one he was carrying was one of them!.
Episode 17 shows Takasugi introduction: he was talking with Katsura about taking down the Shogun during the festival, surprising him since Takasugi started to Laughing Mad. Then it gets worse when while the Festival ends in a terrorist attack, Takasugi surprises Gintoki and starts to talk about the past, specially Gengai's backstory... then Takasugi starts to talk in a creepy way and he says he has the beast of the vengeance inside him and is hearing voices about kill people! showing how wicked is Takasugi.
Sacchan and Okita's ideas on how to improve the series in Episode 50. Specially Sacchan's one.
Pandemoniums also count when they're not seen by Shinpachi.
The Christmas episode in Season 5 that turned into a more frightening atmosphere. Instead of a Santa Festival, it turned to Satan Festival.
Episode 153: the radio story (Jerry the dog). Yeah, it started to he heartwarming and tearjerking, however it ended to have a really twisted ending giving an epic scare to Gintoki!.
Chapter 95 from the manga: Nizou gets fully possesed by the Benizakura and he becomes a full monster.
Chapter 143 from the manga: After some workers sends the maid robots to destruction by being smashed, Number 502 appears and makes stops the robots from obeying orders from the workers and orders the robots to catch the workers. The worst thing is that he sends them to execution by the same way they destroyed the robots!
Chapter 165: Ito thought that he survived without any injuries... however when he looks up and discovers what happened to his arm, he delivers a big scream.
Chapter 219: Kagura entering in Berserker status by trying to stop Abuto from killing Shinpachi and once she reaches that status, is starting to show a creepy smile... leading to Abuto to wonder what went wrong this time while he was getting curbstomped by her. And when he countered her, she was still giving that creepy smile!.
Chapter 255: Jiraiya revealing his face to Tsukuyo and Gintoki. Enough said. Just went worse in the next chapters.
Chapter 401: Just Sacchan's face after taking Sadaharu and the puppy to the house... that was very disturbing since she wanted to kill Sadaharu only to get his skin and then to use it as a wedding dress!!! And it just went worse in the anime!
And now in the chapter 527: The current Shogun Nobunobu was about to decapitate Tae with a wicked smile! And that was after sent to execute 2 innocent women before! Showing how far he can goes in killing people without any remorse!.
Chapter 530 gives some Fridge Horror : If Kondo did open his eyes 1 second later, he would be likely being assasinated by the Naraku soldier since he was silently attacking him!!!
Periphery Demographic: The series is technically shonen, but thanks to its avoidance of most pitfalls of the shonen fighting genre (they don't even have named techniques, much less new ones every arc), deviation from "fight progressively stronger enemies" formula, and an older-than-average protagonist, it's attracted a lot of older fans who otherwise find JUMP comics juvenile. The presence of attractive guys who aren't entirely effeminate has earned it a healthy-sized Estrogen Brigade as well, in addition to a quite large cast of proactive and useful female characters who can fight (and be successful at it) and who aren't the usual flat and ineffectual Fanservice on legs.
Self-Fanservice: Despite a Running Gag of Shinpachi being entirely generic and plain-looking in the actual series, doujinshi artists consistently draw him incredibly pretty. It's surprisingly averted with Kondo and Hasegawa, though.
The Owee Arc displays very little knowledge of even the most well-known Wii gimmicks, and one of the launch titles is a dating sim involving groping, which doesn't really gel with Nintendo's famously kid-friendly image. Truth to be told, the arc was published around the time of the launch of the Wii and it was making fun of the hype around getting one before lampooning video games in general (thus you have Tetris, a dating-sim and an RPG). It wasn't really meant to satirize Nintendo itself.
The Viz Media official translated manga pulled these out here and there. One particular instance involved a character shocked by how terrible a pun was. Rather than come up with an ill-fitting translation, they pointed out that the character made a Japanese pun, and was shocked that someone would do untranslatable humor—"That's the worst kind!"
The upcoming Mexican Spanish dub will possibly have to rely un this. Unlike the English translations, Mexican and Latin American audiences have more tolerance over not-so-literal translations of jokes, as long the jokes are funny.