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.
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, due to them not being allowed to attend following the prank they pulled last year. 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
Ensemble Darkhorse: The cheerleaders from the first book due to their The Woobie status and how they reappeared in the ninth book and one of them got a name.
Fridge Brilliance: Book 12 received a lot of praise for revealing that Future Harold is gay without making a big deal about it. Future George meanwhile has a wife that is only ever referred to as "Mrs. Beard". "Beard" of course is a term referring to a woman that has married a gay man.Have fun with that, fanfic writers!
Dav later confirmed that said wife was actually named "Lisa."
In Wrath of the Wicked Wedgie Woman, it's revealed that the ring was recalled because for unknown reasons, it worked the opposite of its wielder's intentions on women. Unfortunate Implications aside, this might seem like jumping the gun to younger readers, but George and Harold used it on their already-Sadist Teacher and look what happened. Now, what about all the other kids who had one? Chances are, the first thing a lot of them would use it on is their parents, who they typically have a very low opinion of. All of a sudden, there'd be an outbreak of Abusive Mothers all across the country because the kids demand that their every whim be catered to. That wouldn't go unnoticed and would be a pretty damn good reason to recall them.
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.
It Was His Sled: Thanks to the internet, there's no hiding the fact that Harold is gay in the 12th book.
Jerkass Woobie: 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.
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.
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.
The children affected by the Rid-O-Kid 2000.
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.
The Scrappy: Mr. Meaner. A lot of fans didn't like him before, but after Book 12, they quickly grew to despise him.
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 caused unprovoked trouble to not only to the faculty and Melvin, but to their fellow students as well.
In the first book, they ruin a football game For the Evulz, and when Mr. Krupp catches them doing it, he lists off some of their other major offenses during his Evil Gloating (putting bits of dissected frogs in jello at a parent-teacher banquet, making it snow in the cafeteria, rigging the intercoms to play the music of "Weird Al" Yankovic at full blast for six hours), which makes their subsequent punishment seem more like Laser-Guided Karma since they went out of their way to deserve it.
In the second book, they ruin a science fair out of spite because they were (rightly) banned from it due to a prank they pulled the previous year, making their punishment well-deserved.
In the third book, they sadistically torment the science teacher simply because they find his class boring. They also pulled many stunts towards the lunch ladies (the only faculty members who aren't shown to be jerks) such as changing their signs, playing with the lunch trays, making fun of their cooking, and creating comic books about them.
What Do You Mean, It's Not Political?: The books are no stranger to criticizing how public schools treat neurodivergence, 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.
The Woobie: 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 Pilky'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 care more about their scientific work than they do their own son. They didn't even seem to notice that he had become the Bionic Booger Boy until they saw his rampage on TV.
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.