A Boy and His X: "Abner Come Home" from season one was A Boy and His Pig. Season two gave us "Harold's Kitty". "Helga's Parrot" from season four could be construed as a rather twisted take on A Boy, A Girl, and Their Parrot.
Aborted Arc: The Grand Finale never revealed what happened to Arnold's parents. This is because it was going to be the plot of "The Jungle Movie" before a combination of studio politics and waiting for so long that the show lost its popularity caused it to be shelved. Keyboards at the ready, Fan Fic writers!
Also happened with "Helga's Show." Helga was able to do impressions because PS 118 just got a new student lounge. But after that episode, the lounge is neither seen nor mentioned again.
Abhorrent Admirer: Curly to Rhonda, big time. Brainy is a milder version of this trope; his presence annoys Helga to no end but all he really does is breathe down her neck.
Abusive Parents: Helga and the Jolly-Olly Man both have G-rated versions of these. Helga's mother is always passed out on the couch with "smoothies" and never seems to be in a right state of mind. Her father, meanwhile, has a horrible temper, is extremely authoritarian, and is otherwise obsessed with his work. Neither of them pay any mind to Helga, always calling her by her sister Olga's name (who they dote on whenever she's around). Bob and Miriam's (particularly Bob's) treatment of Olga can be considered abusive in a different way. She's a neurotic mess from having to perform all the time "like a wind-up doll" and her perfectionism is implied to be the result of some pretty extreme Education Mama tendencies on the part of her parents. When she got The B Grade, it triggered a nervous breakdown that had her admitting that she would rather be treated like Helga.
The Ace: Helga's "perfect" college-aged sister Olga only looks perfect, but she's dangerously neurotic and melodramatic thanks to having to live up to her parents' constant attention and high standards. She even tells Helga once she'd rather be The Unfavorite since that would let her be free like Helga is. Lila's a parody of this, as well as a general Parody Sue.
Arnold himself can do anything. By the time of the movie, most of the neighbourhood believes he can save them from having to sell up and move. And he does.
Actually Not a Vampire: "Sid The Vampire Slayer". Sid spends the whole episode believing Stinky is a vampire and tries to get proof. When he confronts Stinky, he has a perfectly logical explanation for everything and Sid leaves feeling stupid. Cut to later that night, where we see Stinky, talking to a bat and looking suspiciously like a vampire!
Exemplified on The Longest Monday. The entire Fifth Grade Class participates in a sadistic ritual in slamming the Fourth Graders into trashcans or dumpsters, often rolling them down hills while IN the trashcans regardless of traffic. Not to mention breaking into the Fourth Grader's refuge and even preforming the act on a bus. Where are the parents, schoolteachers, staff? Unknown, no adult is shown at all in the episode.
Truth in Television. adults often overlook yearly traditional hazing rituals in the same vein as the episode. Provided nobody gets permanantly damaged.
Rhonda apparently learns not to be a self-centered libby several times, Olga seems to forget all about her past visits to the Pataki household with each visit, proclaiming her wish to better connect with Helga while unconciously annoying her in all the usual ways.. In one episode, Harold gains new confidence when he learns just how smart he can be if he puts some effort in... next we see him, he's back to being the buttmonkey crybaby of the class.
Justified with Miriam. She learns to be a better mother a couple times; but a couple other episodes make it seem like she's back to her old ways. She relapsed.
At least two episodes had the characters involved immediately forget their aesops before the episode even ended, in one Rhonda isn't invited to a party because she chose to alienate everyone else, at the end of the episode she shows she realizes this was wrong, but before the episode ends quips that the next day she'll be 'popular' again and not a geek like the rest of the party who alienated her for her alienating them, thus showing she really learned nothing. Harold had one where he gained a lot of extra weight and worked hard to lose it, at the end of the episode after losing all the excess weight (not all of it, he was still the Big Eater of the show) he immediately accepts a bet of eating 50 ice cream bars, the same act that caused him to feel bad about himself at the start of the episode.
Hey, remember the episode where Helga and Olga share a touching moment when Olga reveals she hates all the attention and being, as she describes 'Some sort of wind up doll' for their parents and admitting that she wishes she was neglected like Helga? You do? Well apparently both Helga and Olga forgot since their main conflict in every episode is Olga's perfectionism and Helga forgetting how 'good' she has it.
How Helga sneaked in and out of the Sunset Arms in more than one occasions.
The Alcoholic: Helga's mom, Miriam, according to Word of God, but this could only be implied thanks to Nickelodeon's Media Watchdogs. She drinks a lot of "smoothies," talks in a tired, slow voice, looks extremely depressed, is oblivious to her surroundings, forgets things, doesn't drive anymore (and when she did on an episode where Helga and Miriam try to bond during a road trip, she drove rather erratically), and is often found asleep (usually in strange places, like behind the couch or on the living room table). When making a "smoothie", she grabs a bottle of hot sauce.
To enforce this, Helga never seems to find her mother's behaviour unusual or incorrect, implying that it's been going on for so long that to her, it's perfectly normal.
If the spinoff The Patakis had been made, it was said that Miriam would be attending AA.
It has been suggested that Helga merely refers to the booze as 'smoothies' for reasons ranging from basic ignorance, to being told to do so.
Ambiguous Disorder: Arnie, Arnold's cousin. Hobbies include reading ingredient labels, counting things, and collecting lint. He also doesn't seem to know social norms; he asks Rhonda if she wants to see his ball of lint.
Eugene. He has a room decorated with rainbows and unicorns, and often takes interest in anything related to dancing and musicals.
Mr. Simmons, Word of God states that he is in fact gay, but a kids show would never openly state so.
Principal Wartz apparently lived with another man, though it's unclear if this was a partner, a roommate, or simply a visitor. In another episode, Wartz was shown to be excited about a singer mostly popular among young girls.
An Aesop: "Helga On The Couch" taught kids that seeing a shrink isn't a negative thing. Many episodes contained this, really.
Annoying Younger Sibling: Gerald's little sister, Timberly. A more realistic example. According to Jamie-O, Gerald is this to him, but it's incredibly hard to feel sympathy for him when Jamie-O is one of the biggest Jerkass characters of the series. Jamie-O does eventually decides that Gerald isn't as much of an annoying younger sibling after he points out that his relationship is parasitic.
Befriending The Enemy: Some episodes involving Harold, who is a bully to the other kids in his grade are frequently like this. Arnold being an All-Loving Hero befriends Harold in multiple episodes. Even deciding not to rat out on him to the principal in one episode, and helping Harold lose a ton of weight he gained in another episode.
Beneath the Mask: Helga only expresses her feelings for Arnold when alone. (Well, alone with Brainy sneaking up behind her, anyway.)
Beta Couple: In certain Ship Tease episodes, Gerald and Phoebe would hook up in the background. And interview with Word of God stated that had The Patakis gone through, Gerald/Phoebe would've been the "cool couple" to contrast with the somewhat dysfunctional long-distance relationship of Arnold and Helga.
Big Applesauce: The city the show takes place in is pretty obviously based on New York, Brooklyn in particular. Word of God states that there are generous bits of Seattle and Portland, OR mixed in as well.
Break the Haughty: Rhonda, constantly. There are at least three different episodes dedicated solely to the idea.
Broken Aesop: In one episode, Arnold and Gerald play hookey but their fear of being found out interferes with any fun they might have had. Eventually, they go to school only to learn that there was a surprise carnival day. This weakens the Aesop as skipping school is wrong because you miss class, not because you miss a fun day. The "weakness" of the episode's moral is Lampshaded at the end.
In another episode, Phoebe gets to meet pop singer Ronnie Matthews, whom she idolizes for his lyrics which she thinks are deep and meaningful. She's devastated when it turns out he doesn't write or even sing his own music—he just gets paid to lip-sync and pretend to play the guitar. Simultaneously inverts the trope, as this causes Helga to admire him due to how he's managed to make so much money scamming people.
Arnold is not completely safe either (particularly if Helga's involved), and as Eugene, he doesn't have a too hard time handling his problems. This makes him into a No Respect Guy.
Camp Gay: Mr. Simmons is a toned down version of this.
Cassandra Truth: In "Married", Rhonda repeatedly tells Arnold that he will marry Helga (via a marriage predictor). The only one who believes it is Helga, but as per Word of God, they do get married in the future.
Cast of Snowflakes: The art style makes good use of creative head shapes and various body sizes and proportions to make the characters distinctive.
The Cat Came Back: Subverted in "Phoebe Cheats" when out of guilt Phoebe tries to dispose of a trophy she didn't earn. There are logical reasons why it keeps coming back into her possession, but she doesn't see them and she thinks it's moving by itself.
Helga often says "Criminy" when she is frustrated or annoyed.
Grampa's - "Never eat raspberries".
Stinky always either says "this bites" or "this really bites" when something upsets him.
Sid says "boy howdy" fairly often as well.
The word "special" could be considered Mr. Simmons' catch phrase, as he uses it in practically every other sentence. (Which is lampshaded when Helga's impression of him involves using "special" at least five times with finger-quotes.) Ditto for Lila and the phrase "oh so" or "ever so".
Gerald has "Are you thinkin' what I'm thinkin'?" He apparently got it from his father, who does it to Phil in the Veteran's Day episode.
In the April Fools episode Arnold borrows it and turns it around:
Arnold: I think you're thinking what I'm thinking.
Gerald:(whispers in Arnold's ear)
Arnold: That's even better than what I was thinking.
Christmas Episode: the episode where Arnold tries to help Mr. Hyunh find his daughter (whom Mr. Hyunh last saw during the end days of [what's implied to be] the Vietnam War) while Helga tries to buy Nancy Spumoni brand snow boots.
Mr. Hyunh's daughter was never seen again. Possibly justified - after all, she presumably had adoptive parents in the US, given that her father hadn't been in her life for about 2 decades.
Ruth MacDoogal (the sixth grader Arnold had a crush on in the first season) also mysteriously disappears. One could guess that she simply graduated from P.S. 118, since she was already in sixth grade, and Arnold never mentions her (or his crush on her) after the Valentine's Day episode in which Arnold tries to go on a date with both Ruth (who thinks she's seeing a famous poet named "Anonymous") and his French pen pal, Cecilia, and discovers that Ruth isn't all that bright or interesting to be around. In "What's Opera, Arnold?," she appears for the last time mainly for Helga to have a foil in Arnold's dream opera.
Tucker, Coach Wittenburg's son. Appeared in one episode and was never seen or mentioned again. Odd, since Coach Wittenburg gets a few focus episodes. It's particularly glaring when one such episode deals with Wittenburg's estrangement from his wife.
Mr. Smith (the first season border whose face nobody sees) never appears after "Door #16"
Lana Vail, the brunette woman who lived in the boarding house, also disappears midway through the first season, but shows up in background shots on occasion; for example, at the restaurant with the cockroaches in "Dinner for Four". Word of God says that her original characterization was considered too inappropriate for Nickelodeon so they dropped her altogether.
Mr. Purdy also disappeared after only a quick gag in one episode. The boarding house sure suffered a loss of business after season 1.
After "Arnold Betrays Iggy" Iggy never appeared again, reportedly due to Craig Bartlett's hate for the episode.
Circle of Shame: This happens dozens of times. Often, several of the characters forming the circle were laughed at in an earlier episode, because Kids Are Cruel.
The City vs. the Country: Lila moves from a farm to the big city and is immediately resented and made fun of by the other kids. Subverted when she stays in the city and the other kids warm to her.
"Hey! Crazy lady! Come back here with my bulldozer!!"
In the early seasons, Arnold himself was this way, being very quiet and introverted, with a tendency to frequently lapse into intense daydreams.
Principal Wartz, too. During the flood, he dressed in Mexican garb and danced around, then climbed onto the school roof and started singing. He later quit his job as principal for an episode to seek a career as a singer.
Helga's statue of Arnold made out of wads of ABC gum the boy threw away, doubles as a Stalker Shrine.
Arnold's cousin Arnie collects lint.
Ernie has his entire appartment filled with the last brick of each building he demolished (which is over 500). Amazing the extra weight hasn't caused his floor to give in.
Comic Book Time: Not as extreme as other examples, but calenders and signs in the background show the series takes place in the mid to late 1990s. A sign said Gerald Field was founded in July 1997, although the episode aired in October 1996. The It Girl episode takes place in September 1998 due to a newspaper date, and the show Arnold and Helga appear on on their beach trip is filmed in July 1999. The only real other instance of this trope is the fact they have two or three episodes that take place during spring break.
Lila mentions she gets sick on the big amusement rides in "Love and Cheese". After riding the coaster in "Timberly Loves Arnold" she's seen throwing up.
There's a couple in the movie involving the episode "Dino Checks Out." Out of his album covers spoofing The Doors Strange Days is seen in Grandma's jail cell, and the Dino Impersonator is seen in the bar Arnold and Gerald sneak into.
The premise of "Beaned" calls back to the plot of "Dangerous Lumber," showing that Arnold still has a perfect record for beaning people with baseballs. And the plot of "Dangerous Lumber" could be seen as continuing off of the event that kicked off "24 Hours To Live."
In the episode where Arnold tries to help Chocolate Boy overcome his chocolate addiction Gerald mentions several of Arnold's past accomplishments which were all from past episodes.
"Helped Stoop Kid and The Pigeon Man, found Mr. Hyunh's daughter, saved Mighty Pete, stopped the teachers strike..."
Corrupt Corporate Executive: Sheck in the movie, who isn't above burning a historical document declaring the neighborhood where the main characters live as a national landmark just to build a huge mall.
Technically that wasn't corruption, that was revenge. As he wanted to destroy that neighborhood because that's where his ancestor lost.
Curly, and his Troubling Unchildlike Behavior sometimes comes to the point of high-potential Ax-Crazy. Upon finding that he wasn't assigned the Ball Monitor privileges that he anticipated for that week, he holed himself up in the principal's office with the balls, throwing them at anyone who tried to reason with him. He tried to get Eugene expelled simply because he ruined his favorite pencil. Curly's Stalker-iffic admiration of Rhonda intersects with this trope more often than not.
"SO HOW ABOUT A LOCK OF YOUR HAIR TO KEEP UNDER MY PILLOW?"
Stoop Kid. The neighborhood kids are rightfully scared of him.
Dark-Skinned Blond: Nadine. This becomes a bit more...somewhat plausible when you notice that in Parent's Day, her dad is white and her mom is black.
A Day in the Limelight: Despite his name being in the title, there are more than a few episodes where Arnold has absolutely no connection to the plot at all.
Indeed, by the end of the series, it's easier to count the secondary characters who didn't ever get an episode focusing on themnote Sheena, Park, Joey; practically every kid in Arnold's class and "permanent" member of the boarding house had at least one.
Dead Artists Are Better: In an in-universe example, one episode involves Dino Spumoni faking his death to rekindle an interest in his music and raise his sales. It works too well as a Dino-impersonator comes along, doing his songs and gigs, dates his wife, and his dog loves him, and drives Dino jealous and reveals he isn't dead.
Deadly Euphemism: Grandpa and Jimmy Kafka exchange a bunch of these in "Old Iron Man" when they believe they're about to drown.
Deceased Parents Are the Best: Arnold's parents, Miles and Stella, are assumed to be deceased. Whether they are or not, they fall squarely into the trope, having devoted their lives to working with and healing the inhabitants of remote jungles. In the ultimate saintly move they left Arnold with his grandparents after being pressured to go on one last mission—and never came home.
Deconstruction: Arguably for shows like Arthur and Recess. For in those shows, there is a memorable/colorful cast of characters, all with their own personality quirks. While that is present here in Hey Arnold, the quirks and traits that make the characters more or less memorable, are usually the result of some hidden neurosis, or psychosis. Some characters have even received therapy for said problems; only to regress to their former problematic ways at the story's end.
Defeat Equals Friendship: Subverted in the episode "24 Hours To Live" because even though Arnold never fought Harold directly, he still gained his respect after the "fight" sequence, through the way he got himself out of the fight.
Depending on the Writer: A lot about the way the kids relate to one another change depending on the plot - which makes a bit of sense for grade school kids. Most obvious is how close the gang is: sometimes they're one huge tightly knit group of friends, other times they seem more like just classmates with their own cliques. This is particularly the case with Harold and especially Helga - one episode might have them treated more as bullies and be somewhat separate from the others, while other episodes might have the others treat them as regular members of the gang who just happen to be jerks. This also extends to Helga's relationship with Arnold - sometimes he sees her as a bullying nuisance and doesn't seem to like her very much, whereas others make it more evident that he is aware her abrasive attitude is a cover of some kind and approach her as a friend regardless of her behavior (compare "Helga vs Big Patty" with "Egg Story," for instance). Notably, the True Companions approach to the characters is most often used in episodes where they go on some kind of adventure, and got a bit more common in general episodes as the show went on.
Helga at times, particularly when her secret is in danger of getting out. The climax of "Helga's Parrot" in particular has her single mindedly driving herself through the roof to keep things under wraps.
Dinner Order Flub: Helga, trying to pass herself off as Arnold's French pen pal whilst in disguise and with a very rudimentary knowledge of French, attempts to make a order from the menu of a fancy French restaurant. It isn't until she's happily tucking into the dish that the waiter informs her that she's eating cow brain and eggs... which prompts a dart to the bathroom. Arnold played it safe with a steak and fries.
Disappearing Box: Helga gets involved in the trick, but decides to run away instead of staying behind the secret wall, thinking what life would be like without her. It leaves Arnold trying to bring her back many times with no avail.
Averted with Helga. While her bullying (of everyone, not just Arnold) is not treated as seriously as a male bully would be, it is still not portrayed as being okay by the show, pointing out repeatedly that it is a problem, and that what Helga is doing is not acceptable behaviour for anybody.
Helga on the Couch: Principal Wartz didn't seem to pay much attention to Helga punches Brainy, as usual, until Dr. Bliss informs him of this. It's possible that Wartz, like the students, had grown custom to it or reports didn't get reported considering how Helga is.
However, in one episode, Helga throws glue on Arnold, and Arnold snaps and throws paint on her. Arnold is the one who gets yelled at.
Played straight with Arnold's grandparents when they were kids, where his grandmother would do the same (if not worse) to his grandfather.
Downer Ending: "Arnold Betrays Iggy", "New Bully on the Block", and "Operation Ruthless."
"Operation Ruthess" is later revisited with "Love And Cheese," which has the same basic plot, but replaces Ruth with Lila, and ends the same way but as even more of a downer for Helga (admittedly, she brings it on herself both times and shouldn't be allowed to get away with what she does, but both endings portray her as so pitiful that you can't help but feel for her.)
The show as a whole arguably has a downer ending where Helga is concerned, since there's little indication of her family life getting any better or her becoming any nicer or confessing her attraction to Arnold (except in the movie, but then she denies it at the end). Still, "Helga On The Couch" implies that she could be a happier and better person with Dr. Bliss' help and encouragement, and Word of God says that Arnold and Helga get married at some point in the future.
The first season is a lot different from the other seasons. The animation is of much lower quality, with lots of Off Model scenes, there are less episodes centered around Helga, Arnold has a crush on Ruth, who is nowhere to be found after season 1, and on top of all that, Arnold is FAR more child-like and immature compared to the later seasons.
Easy Amnesia: Helga gets amnesia after getting hit with a baseball. Subverted in that she gets her memory back normally when she wakes up the next day, not by getting hit again. However, she continues to fake amnesia to take advantage of Arnold's kindness, and when she feels guilty about it, she intentionally hits her head again so she can pretend that she just then got her memory back.
Election Day Episode: Marty Green, a butcher shop owner, angry at the fact that his councilman was failing to do things to help the community he represented (such as failing to get funds to repair and repave roads which had massive potholes) and spent more time golfing than working on legislation, decided to oppose him in the upcoming election. Green wins.
Big Bob's greedy, but he's not a murderer. He also refuses to bulldoze a tree upon realizing there were kids up there, but mostly his kid (which in of itself is something, considering how neglectful he usually is of Helga.)
Helga gives Arnold a lot crap but during the parents day episode when Bob calls Arnold (who was in earshot) an orphan, she is shocked and later goes up to Arnold and apologizes for it, justified because it's probably one of the only things that can hurt him.
Played with when Rhonda (forced by circumstance to pretend to be his girlfriend) publicly dumps Curly and humiliates him, Helga is disgusted with her and tells her she has a black heart. To Rhonda, Helga is the biggest Jerkass around (only the audience knows about her hidden heart of gold).
Everyone Went to School Together: In this case, they all went to pre-school together, as revealed in a flashback in "Helga on the Couch." Strangely, even Harold was there, even though a previous episode had made Harold several years older than his classmates.
Evil Laugh: Curly wins in the best psychotically evil laugh department, but Helga has a pretty impressive one as well. Some of the other characters get one in certain episodes: Sid for example gets on in "Sid's Revenge," and Phoebe gets a brief but creepy evil chuckle in "Phoebe Breaks A Leg."
Evil Plan: Helga, often with episodes dedicated solely to her pulling series of them. A running gag in the series is that her evil plans always fail in ways that only help the person she's trying to hurt and hurt her instead.
Extreme Doormat: Phoebe takes everything Helga throws at her - however, she gets some Character Development, in a few episodes where it's shown Helga also depends on Phoebe's support.
Arnold himself is like this a few times.
Expy: Ronnie Matthews seems to be a one-man version of Milli Vanilli. Handsome dark-skinned guy? Check. Strong European accent that disappears when he "sings?" Check. Complete inability to write and/or play music? Check, check and check.
"Jungle Movie" fanfics, write-ups, and speculatory scenes are very popular. Especially since "The Jungle Movie", had it ever been made, was supposed to resolve both the plotlines mentioned above.
Hey Arnold! fanfics are also particularly fond of the plot where a character (usually Helga, but used at least once for everybody) leaves/runs away from town, stays away for years, and then comes back to meet their old friends all over again, until the end of the story where they find their Love Interest again and hook up.
Fail O'Suckyname: After Eugene manages to wreck his and Arnold's go-karts in the go-kart episode, they have to combine their kart names... cue "The Mauve Avenger", which Gerald absolutely hates. Apparently naming the kart its other combination, "The Dark Storm," never crossed their minds.
Feud Episode: "Best Friends", between both Arnold and Gerald and Dino Spumoni and his songwriting partner.
Arnold's desire to help out others and completely incorruptible, Confucius-like personality.
Helga's obsession with Arnold.
Eugene's bad luck intensifies with each passing season.
Grandma started out eccentric and a little batty, but ultimately sane and always willing to give Arnold a little advice (even if it was delivered in a non-traditional manner), but she got slowly crazier as the series wore on and by the end of the series she's little more than a crazy old lady who lives in Arnold's house.
Olga started out as overachieving drama queen that would actually be treated like Helga if she wasn't successful and understood Helga's plight to.... just a content, overachieving drama queen. Also, you'll be damned if you see Miriam functioning despite drinking and scouring the city to get Helga a sold out gift for Christmas in any later season.
Sid went from a fairly nondescript supporting player to a paranoid nutcase as the series went along. Episodes focus on his fear of germs, vampires and casting a spell on Principal Wartz.
Free-Range Children: The nine-year old cast runs about the city (which is quite big, mind) with little concern from any of their parents. This includes playing sports in the middle of a busy street, running away when a car comes. This particular instance doubles as Truth in Television.
Freeze-Frame Bonus: If you pause in "Phoebe's Little Problem", you can see that apparently they have school over the summer. Maybe they're making up the days they missed from the Teacher's Strike?
As seen in one of Helga's days in the limelight, "Helga on the Couch." She discusses with the school psychiatrist her obsession of Arnold which is deeply embedded into her family life. On her first day of pre-school her parents were more focused on her sister Olga playing the piano. They didn't even acknowledge her existence when she asked them to bring her. She had to walk there herself and on the way it began to rain, mud got splashed on her, and two rottweilers stole her lunch. Then Arnold gave her his umbrella, which was possibly the first time somebody showed her genuine kindness. She began her assertive personality when Harold teased her about the crush. She explained to the psychiatrist that she treats Arnold the way she does because she fears rejection like how her family seemingly rejected her. It's safe to say that not one member of the audience had a dry eye when the episode was over. And Helga was placed top of the show's Woobie list.
Parodied with the Jolly Olly Man: If you had to drive dialy to a wasteland of a city to sell ice cream to horrible children you will be a little crazy too (even more scary, the true source of his problems is his father, who doesn't believe in him and is clearly expecting him to fail).
Frothy Mugs of Water: Miriam is (un)ambiguously alcoholic. She's shown drinking "Smoothies" and falling asleep in odd places, as well as putting Tabasco Sauce in them. She has slurred speech and signs of depression.
Averted in "Buses, Bikes, and Subways" when Mr. Simmons' class sings the "explicit" version of "99 Bottles of Beer on the Wall."
Funny Foreigner: Mr. Hyunh has shades of this at times, but Oskar Kokoshka defines this trope.
Sid: I bet [Rhonda] thinks I'm a geek because of my big nose!
Stinky: It's not that big.
Sid: Thanks, but you're only saying that because you have the biggest honker in the world. No offense.
Stinky: None taken.
Gay Paree: Subverted. When Helga tried to pass herself off as Arnold Pen Pal. He asked about her home and Helga responded that Paris is a big noisy city, full of french people. Then Arnold recalled Cecile saying that she lived in a farm, catching Helga off guard.
God: Appears in Stinky's prophetic dream in "Stinky's Pumpkin", voiced by Tony Jay
Good Parents: Surprisingly, most of the cast members, except Arnold and Helga, have these. Some kids are shown only with one parent, but it's generally assumed the other one is there and simply not relevant to the plot.
Gosh Hornet: In "Helga's Boyfriend" when Helga gets attacked by bees at the park.
Granola Girl: Is Helga's nickname for Sheena, which seems to be more or less accurate.
Chocolate Boy's obsession with chocolate is very similar to a drug addiction. In one episode, he begs Arnold to help him get over this. It is revealed that his nanny who took care of him as a very young child always gave him chocolate. He was devastated when she was forced to leave him. He ate chocolate to remind him of the one person who ever loved him.
Stoop Kid somehow manages to be both this and a gutterpunk at once.
Arnold becomes this when he loses his hat, saying that he'll never come out of the house without it.
Hollywood Voodoo: In one episode, Principal Wartz gives Sid detention for a prank he didn't pull. Out of revenge and his frantic paranoia, Sid carves Wartz' likeness into a bar of soap. The next day, Sid finds out that Wartz is in the hospital, and is told by the doctor that he's already "checked out." Following this is a string of signs that soap voodoo worked. Hilarity Ensues.
Homage: 'What's Opera, Arnold?' was a Homage to the opera Carmen, right down to altered song lyrics. It's also an homage to the Bugs Bunny cartoon, "What's Opera, Doc?"
Homeless Pigeon Person: A "pigeon man" (trope picture) lives on a rooftop, with some elaborate cages containing hundreds of pigeons. At the end of the episode, he actually flies away carried by his birds.
Hourglass Plot: Happens to Phoebe and Helga in "Phoebe Breaks A Leg" - when Helga is indirectly responsible for Phoebe getting injured, out of guilt she starts waiting on her in the way she often had Phoebe wait on her. In a twist, Phoebe quickly realizes this is happening and - tired of being treated like an assistant all the time - conspires to keep it that way for as long as she can.
Huge Schoolgirl: Big Patty. Also Sheena, who's as tall as most of the adults on the show.
Humiliation Conga: Helga tends to get these in episodes where her evil schemes go south in particularly unpleasant ways. Rhonda, as well, gets pretty severe ones in episodes where she's particularly haughty.
Hypocritical Humor: In "Gerald's Tonsils" Gerald tries to practice singing with with his new post-tonsillectomy voice and a kid overhears him and makes fun of it, saying he has a "crazy voice." The kid has a very annoying and nasally voice himself.
"Girl Trouble" features this classic bit from Pookie.
Pookie: Just remember, Arnold. Violence is not the answer.
She karate chops a watermelon to slice it, hard enough to splatter some of it across the wall.
"Spelling Bee" has a banner hung outside the location holding the titular spelling bee. What does it read? "WELCOME SPEELERS!"
I Can't Believe It's Not Heroin: In one episode, Arnold helps chocolate boy quit his "obsession" with chocolate for two weeks, only to get a 10 pound bag of chocolate. After chocolate boy realizes how pathetic he has become, he wants to quit for good. Chocolate boy's mannerisms in this episode are very similar to a crackhead. Justified somewhat by the sheer quantity of chocolate Chocolate Boy consumes. Child or adult, that much caffeine and sugar will mess you up.
Ineffectual Sympathetic Villain: Helga in episodes where she's antagonistic, particularly as the series goes on. Especially noticeable in episodes involving Lila. The series does this especially well: because we know Helga's true insecure reasons for doing what she does, when her Evil Plans to humiliate Arnold or Lila or whoever's incited her jealous wrath fail epically and/or backfire hilariously on her the audience laughs, but also feels truly sorry for her.
I Was Beaten By A Girl: Harold by Big Patty in an arm wrestling match. He is so upset, he attempts to escape from those mocking him by hiding under a drinking fountain. He finally gets over it by the end of the episode - after she beats him again in the citywide arm-wrestling championships - and smacks Sid and Stinky together when they trash talk about him after his loss, but not before publicly defending Patty as the better opponent. (The end of the episode implies a Relationship Upgrade for Harold and Patty due to this.)