Americans Hate Tingle: Although the series has garnered controversy in its home country of America, it is even more hated in Japan, due to the boys' constant pranking and irreverence to authority clashing with Japanese morals of quiet obedience. It does not help that almost every single authority figure is portrayed as an antagonist. This lead to the movie only getting a direct-to-video release, and the cartoon being obscure in general.
Anvilicious: Dav will never let you forget that kids need imagination and fun in their lives and it plays as much of a role in their future as having an education.
Crosses the Line Twice: Teachers abusing their kids isn't funny in theory, but when said abuse involves stealing their lunches and making them write lines like "I'm so ugly, when I was born, the doctor slapped my mom", it becomes hard not to laugh.
Designated Hero: George and Harold have a tendency to slip into this with some of their pranks. In the first book, they cause enough disruption at a school football game to get the school to forfeit it, and subsequently ruin everyone else's day, and Captain Underpants is later created as a result of their attempt to avoid being punished for this. In the second book, they sabotage the school's Invention Convention out of spite because they were banned. Why were they banned? Because the previous year, they played a prank on the teachers and every other student by secretly gluing them to their chairs. These only apply to the first five books, however. As the books continue, we see more outside threats not by them or by returning villains.
Kipper Krupp and his friends have garnered a bit of popularity amongst fans despite only appearing in Book 9.
Dog Man. After briefly being mentioned in the first book and having a comic book written about him in the ninth book, he got so much fan art that Pilkey decided to bring him back for the last two books, and eventually gave him an entire spinoff.
Growing the Beard: The series started out as just simple harmless children's entertainment and little else. However, by the 4th and 5th books, Dav's commentary and messages become clear to more observant readers, with just enough subtlety to keep smaller readers entertained but still encouraged.
Heartwarming in Hindsight: In the library where the boys traveled to a different dimension, one of the books parodies the controversial children's book, Heather Has Two Mommies. Then in the 12th book, Harold marries a man with two children.
Book 9 sees George and Harold make a comic book for their respective grandparents about how awesome they (and old people in general) are. The grandparents are clearly touched by this, and even emulate the comic to save the boys in the end.
In the original EPIC NOVEL, Mr. Krupp talks of a Noodle Incident involving George and Harold rigging the school intercom to play "Weird Al" Yankovic music. Years later, he composed and performed the movie's theme song.
In Book 3, the boys have to deal with an army of Zombie Nerds. You cant help but wonder if Tom Warburton read this one, seeing as how an episode of Codename: Kids Next Door has almost the exact same premise.
Professor Poopypants. He just wanted people to stop laughing at his name, though George and Harold point out that he could have simply changed it rather than forcing everyone else to change their name into something ridiculous.
All three versions of the professor have there moments in book 10. Big Tippy refuses to let either of the two Tiny Tippies help him catch Captain Underpants. The two Tiny Tippies travel to the future to use there inverseShrink Ray to grow to there normal height so they can help Big Tippy. When Tiny Tippy grows to his normal height, he then uses the machine to grow to twice his normal height, renames himself "Supa Mega Tippy", and refuses to let Slightly Younger Tiny Tippy use the machine. Upon returning to the past, Supa Mega Tippy also betrays Big Tippy, directly causing his death.
LGBT Fanbase: A curious case, as the LGBT people who are fans of the series are primarily made up of people who actually read the books as children, before realizing they were LGBT, but have since flocked back to the series in recent years, both out of nostalgia and after the reveal that Harold turns out to be gay. It helps that the long hiatus gave a lot of the early readers time to grow up and "grow out" of the books, before said reveal revived their interest.
Moral Event Horizon: Tiny Tippy steps close to the line when he becomes Supa Mega Tippy and leaves Slightly Younger Tiny Tippy in the future, and eventually crosses it when he steals Captain Underpants from Big Tippy and leaves the latter to get blown up by his own bomb.
Nausea Fuel: Inevitable in Toilet Humour-themed series, but the Bionic Booger Boy gets special mention. His descriptive introduction is cut off when George yells at the narrator for making everyone sick.
The Bad Future created by Tippy Tinkletrousers. On top of this disaster-layer cake, we also saw gigantic zombie nerd-versions of George and Harold. Also from this section of the book, Tippy is crushed, blood and all. Doubles as a Tear Jerker. Thankfully, the last bit (Tippy's death) is averted in the sequel, and it's revealed that the thing that got crushed was a giant ketchup packet.
The narrator might be right to the fact the fight between Melvin and the Turbo Toilet 2000 may give anybody nightmares. For WEEKS.
The children affected by the Rid-O-Kid 2000, being stoned faced, robotic and mindlessly obedient to adults (Mr. Meaner even has a Last-Second Word Swap in his commercial where he calls them slaves). What's worse? Every single adult in Piqua is perfectly okay with and even supports this.Including George and Harold's parents after past George and Harold get affected by it.
Older Than They Think: Dav Pilkey's first drawing of Captain Underpants dates all the way back to the very events that inspired him in second grade. He drew the character in class after his teacher outright said that underwear isn't funny. When he was sitting in the hallway as punishment, he proceeded to draw an entire comic book of the character! Sadly, both of these were torn up in his face by his unamused teacher.
Periphery Demographic: The books have a lot of teenaged and even adult fans — both people who read the books for the first time as kids and simply never stopped enjoying them, or people who read them to kids, and found that they could enjoy the more clever, subtle humor and social commentary while the kids enjoyed the superheroes and toilet jokes.
In-universe (and out for the readers) in Book 6. The Narrator's description of Melvin gets grosser and grosser until George yells at the Narratorto stop.
Taken Up to Eleven in (appropriately enough) Book 11, where the boys convince all of the teachers and faculty that they're in a dream. This prompts the grownups to release their inhibitions by performing all sorts of shenanigans in their underwear. And yes, Dav Pilkey illustrates this repeatedly...
Strawman Has a Point: While the school faculty and Melvin are deliberately written to be unlikable and get kicks of making the students miserable, their animosity towards George and Harold does serve good points (as mentioned above and below). The boys often cause unprovoked trouble to not only to the faculty, but to their fellow students as well. And as the second book shows, that includes the ones who've never done anything to provoke them.
Unintentionally Sympathetic: Melvin is deliberately unlikable, but there are a few fans who side with him because George & Harold do go too far with their antics.
Values Dissonance: The books paints medication for ADHD and similar mental disorders in a very negative light. In recent years, looking down upon medication and people who use it can easily be seen as ableist, as medication has not only proven to be safe and effective when used correctly, but borderline necessary for certain people.
They Wasted a Perfectly Good Plot: With how the book series ended, a lot of fans felt this way about Krupp and Captain Underpants never finding out that they were one and the same. It could have led to some interesting storylines with the two and might have given Krupp some character development.
What Do You Mean, It's Not Political?: The books are no stranger to criticizing how public schools treat conditions such as, (and especially) ADHD. Book 12 in particular makes a Bland-Name Product version of Ritalin (the villain's mind control gas that suppresses creativity and individuality). The same book makes reference to the GOP hating people who are young and different from them. In this case, it stands for Grumpy Old People, but American readers will recognize the acronym as that of the Grand Old Party, AKA the Republican Party.
Kindergartner Harold. His dad's gone before the book starts, he's bullied on a daily basis, and it's all but stated he draws constantly because of everything that's happened to him. It's no wonder he's friends with George after the kid saves him.note Even sadder, this is all taken verbatim from Dav Pilkey's actual childhood (save the Disappeared Dad).
Melvin could possibly count as a Jerkass Woobie (at least before he Took a Level in Jerkass from Book 7 onwards), as it is kind of implied in Book 6 that his parents are such workaholics, that they come across as somewhat neglectful of their only son. They didn't even seem to notice that he had become the Bionic Booger Boy until they saw his rampage on TV. And he had been the Bionic Booger Boy for what just might possibly have been a few months at that point!
Esoteric Happy Ending: The ending of The Invasion of the Potty Snatchers. Billy and Diaper Dog stop Rip Van Tinkle from destroying the city, but they never actually solve the lack of toilets problem, when the lack of toilets was the main conflict of the book in the first place. Despite this, the ending is still presented as a "happy" one.