- Author's Saving Throw
- One of the complaints from the movie is that both Harold and George sounded too old for elementary school aged boys. The series however brought back Children Voicing Children for most of the child characters.
- Some fans who felt like the movie watered down the anarchistic spirit of the original books have said that this is a better adaptation for the screen, as it not only brings back much of the beloved Toilet Humor but also bares a close aesthetic resemblance to them (alliterative chapter breaks, lemony narration) without eschewing the well-received Character Development and art shifts from the movie.
- Another complaint was how Melvin's possible redemption at the end of the season 2 finale was ruined in the season 3 premiere where Melvin goes back to being an unsympathetic antagonist for the entire season. The Halloween Special somewhat remedies this by having the boys invite Melvin to go sneak-or-snacking with them which in turn softens the nerd's heart because of their thoughtful gesture.
- Accidental Innuendo: "Who's pumped to dump?!"note
- Broken Base: The comic book narrations. Some think the deliberate badness is hilarious and fitting, other think it's trying too hard and goes much too fast.
- Crosses the Line Twice: Mr. Ree's backstory in episode 5. What else can you say about a backstory where multiple people are apparently mortally wounded by paper cuts?
- Die for Our Ship: Thankfully averted with Ms. Yewh. During her appearance, many fans felt uneasy when Mr. Krupp fell madly in love with her since they preferred to ship him with Edith the Lunch Lady. Unlike Edith however, Ms. Yewh shows no romantic interest in Mr. Krupp and ends up having a crush on Mr. Ree, the school janitor.
- Ensemble Dark Horse: Bo Hweemuth has proven to be one of the most popular characters on the show thanks to his sympathetic backstory and how much of a lovable, good-hearted boy he is.
- Evil Is Cool: Second only to Poopypants, Melvinborg has become increasingly popular in the fandom.
- Fan-Preferred Couple: George/Harold/Melvin, Bo/Gooch, and Erica/Jessica/Dressy all have notable fanbases.
- Fanon: Two popular headcanons among the fanbase is that George is bisexual and that Melvin is a trans boy.
- Foe Yay: In "Captain Underpants and the Shadowy Syndrome of the Sinister Splotch", Captain Underpants makes a few comments towards Splotch that came across as a little flirty.
- Genius Bonus: In the season 2 episode "The Dastardly Deeds of The Devious Diddlysaurus" George and Harold enter the time toad and a few dates fly across the screen: 1999AD, 1475AD, 79AD, and 753BC. The scene is quick enough that one might think they're random numbers, but if you're familiar with Rome you'd realize they're all important dates in its history: 1475 was when the Empire is considered to have officially ended, 79AD was the eruption of Mount Vesuvius, and 753BC is when Rome was supposedly first founded.
- Harsher in Hindsight: In the movie, there is a scene where Captain Underpants is terrified of a bee that a shrunken Poopypants is riding on and swats it away. In Season 2's, "The Harmful Horrors of the Harrowing Hiveschool", we find out he's allergic to bees.
- Hilarious in Hindsight: The initial conversation between Ms. Yewh and Mr. Ree when they first meet at the end of their debut episode becomes this after we discover Mr. Rees first name in Season 3.note Ms. Yewh: Where am I? And whats that smell?
Mr. Ree: Smells like victory.
Ms. Yewh: No, it smells like a toilet.
- Jerkass Woobie: Much like with the movie, Mr. Krupp falls into the this territory, especially after episode 11, where we finally meet his mother and get a glimpse of what his childhood was like.
- Launcher of a Thousand Ships: So far, Bo has been looking like this. While theres the Fan-Preferred Couple of him and Gooch, the show itself has given us Ship Tease between him and both Other Sophie and Dressy, with those pairings getting fans as a result.
- Narm Charm: Like the books and movie it's based on, most of the humor comes from running with the silliest, most juvenile ideas imaginable, and it works.
- Nausea Fuel: The scene in episode 6 where Mr. Krupp eats spoiled guacamole that the boys made as a prank (even though they warned him not to), and then proceeds to extensively throw up (twice!) behind his desk. And if that werent enough, he then slips in his puke.
- Nightmare Fuel: The creepy ventriloquist dummy that resembles Mr. Krupp. It borders on Uncanny Valley territory.
- In season 3, we get a recurring stop-motion clown called Gigglenose who comes with his own disturbing circus music.
- Padding: A majority of the jokes tend to run on much longer than needed.
- Rescued from the Scrappy Heap: Mr. Meaner was highly despised as a result of what happened in the twelfth book, but this series helped get him back in the fandom's good graces, mainly because of his hilarious lines.
- The Scrappy: Bernice, Mr. Krupps mother, quickly became this among fans.
- Ship-to-Ship Combat: Thankfully averted with the Bo x Gooch shippers and the Bo x Other Sophie shippers. Both sides are more than willing to respect the other's preferences and there has yet to be any serious fighting between the two groups.
- The above-mentioned puking scene in episode 6.
- Melvins Mom flirting with Smartsy Fartsy (who, may we remind you, is a sentient fart) in episode 13.
- Toy Ship: All the ships listed above fall under this category since they all consist of children.
- The Un-Twist: Grace Wain is Erica Wang's future self. Considering that we were introduced to Melvinborg in the Season 1 finale along with how Erica is always 3 steps ahead of everyone, the reveal was a little anticlimactic.
- They Wasted a Perfectly Good Character: Fans are starting to feel this way about Mr. Krupp. Thanks to The Movie giving a more sympathetic portrayal as a lonely Jerk with a Heart of Gold along with the season 1 finale showing a few hints of potential redemption, there was hope that Krupp would get significant character development and change into a better person. But 3 seasons and a holiday special later, fans were disappointed to find how Krupp is still the same cruel-hearted, idiotic, self-serving jerkhole who is still able to get away with tormenting the children and just about everyone else around him without consequences.
- They Wasted a Perfectly Good Plot:
- Most fans have this sentiment for "The Soggy Salvation of the Swirling Sweatnami". While it does a great job in exploring Mr. Krupp's backstory and explains why he's so full of hate and wickedness, it tarnishes the possibility of him becoming a genuinely good person if given the opportunity. This is further cemented when Erica at the end claims that Krupp was just "born evil" and how George and Harold decide that it's futile to try and help him.
- A lot of fans felt this way about the Season 2 episode The Bombastic Blathering of Brainy Blabulous, as it wouldve been a perfect opportunity to basically be the 8th book in animated form, but they never capitalized on it.
- The Woobie:
- With how much of a Butt-Monkey he is, you cant help but feel kinda bad for Jerry Citizen. Even George and Harold felt guilty when a prank they pulled on him drove the poor man to tears.
- Bo Hweemuth. Until George and Harold help him out, he gets saddled with a reputation that paints him as a fearsome bully, all because he spends most of his time alone in the ceramics room. Then, when he finally befriends the other kids, Melvin kidnaps him and turns him into a mindless clay monster.
- Other Sophie. Compared to Sophie One, Jessica treats her badly most of the time.
- What an Idiot!: Jessica and the other kids mistaking a tree sloth for Other Sophie in the second episode of Season 2, and not realizing it until Other Sophie came back as Queen of the Croco-Bats 5 episodes later.
YMMV / The Epic Tales of Captain Underpants