Ageless Birthday Episode: Averted in "Boys in the Band" (as "Abra-Catastrophe" states that he was about 9 when he got Cosmo and Wanda), and A Fairly Odd Movie: Grow Up Timmy Turner. Played straight in "The Fairy Flu" and "Birthday Wish!" for Tootie and in "Birthday Bashed!" for Timmy.
Alliterative Name: Timmy Turner, Trixie Tang, The Crimson Chin, Doug Dimmadome and the list goes on.
In the case of Mr. Dimmadome, the alliteration has also become a prevalent Running Gag.
Doug: I'm Doug Dimmadome, owner of the Dimmsdale Dimmadome!
All-Cheering All the Time: Fairly Oddparents had a competition wherein Timmy sabotaged Vicky. Her cheer was all her gross habits. The girl who won improvised a cheer indicating that she had none of Vicky's gross habits.
All There in the Manual: The special The 77 Secrets of the Fairly Oddparents revealed, among other things, Cosmo and Wanda's full names.
Allergic to Love: Chester gets "the hives" from girls, while Mark Chang's entire species is biologically averse to love or even cuteness.
Almighty Mom: Mrs. Turner tries this occasionally, especially in the earlier episodes.
To the point where her super-powered persona occasionally wished up by Timmy is named "Mighty Mom", and in the episode where Timmy first makes the "Mighty Mom and Dyno-Dad" wish, their explicit cause for fighting crime is summed up by Timmy's Dad:
Mrs. Turner: "We don't have time for Timmy...we're trying to make the world safe for Timmy!"
Almost Kiss: Several between Timmy and Trixie in Wishology Part III.
And I Must Scream: Every Unwished Wish is put into storage, even if they're sentient. And they live forever... Oddly subverted after Timmy discovers the island where most of his unwished enemies/objects end up. He makes a few wishes to ensure that the island is as comfortable as possible for everyone trapped there. These improvements include luxurious resorts and servants in his image that accept physical violence as payment.
Anticlimax Cut: When Timmy, Cosmo and Wanda entered a scavenger hunt, one of the items was a Pot of Gold from the 15th century. Timmy commented on how leprechauns are usually protective of their gold. Cut to a leprechaun willingly giving them his pot.
Back to School: episode "The Old Man and the C Minus", Timmy's Dad entered a Game Show titled Are You Brighter than a 4th Grader? and lost because he answered "sea cucumber" to all questions except the one where "sea cucumber" was the right answer. He then admitted he didn't finish fourth grade and his wife forced him to go back to school to set an example for their son.
Bad Future: The beginning of Channel Chasers, where Vicky has taken over the world.
Barbaric Bully: Francis. He's about twice the size of everyone else at his school, he wears heavy chains on his clothes, he has grey skin, he apparently feeds first graders to his dog, and he's brought medieval weapons to school on at least one occasion. You know...just like bullies in real life.
Along with Trixie in her Wonder Gal outfit, Veronica in her Wardrobe Malfunction, and few of the female students in Dimmsdale Elementary are like this too, the school itself has rather lousy dress code for allowing ten year olds walk around with their belly buttons revealing.
Beauty Is Never Tarnished: Zig-zagged in "Just Desserts". After everyone has turned fat, the only recurring females we see are Wanda and Trixie. Also, unlike most of the guys and Wanda, Trixie isn't grossly fat.
* Beggar With A Signboard: used twice. In the Season 1 episode "The Big Problem", Timmy says that one advantage of being an adult is not needing a babysitter. In his Imagine Spot, Vicky is on the street corner, holding up a cup and a sign that says, "Will babysit for food". The handsome adult Timmy stops by and puts a coin in the cup, then pulls it away, as the coin is attached to a string. As he does this, he says, "Psyche!" to Vicky and drives away. In the Season 5 episode "Timmy TV", after his own show, "Leave It to Binky", is cancelled, Binky ends up on the streets holding a sign that reads “Will act for food”.
Berserk Button: Fairies, for Timmy and Crocker: Timmy, if you do bad things to them; Crocker, if you so much as mention them.
Poof has one, too: Don't do bad things to his parents.
Betty and Veronica: Tootie and Trixie. You Doo and Take and Fake are the two only episodes where Tootie is aware of Timmy's crush on Trixie.
Trixie also has a friend who is actually named Veronica, and the story plays out the same way. Ironically, Veronica seems to play the "Betty" role.
Big Ball of Violence: often played straight and parodied, but used in a very egregious way in Twistory, when Washington and Arnold beat the crap out of each other, accompanied by the inevitable Unsound Effect: "FIGHT FOR FREEDOM!"
Book Dumb: Timmy barely goes beyond an F. However, this could not entirely be his fault, since his teacher, Mr. Crocker, is obsessed with giving everyone in the class F's (save for AJ). In a few episodes he actually does pull out good grades on his assignments.
Crocker: This assignment is very well written! But I'll give it an "F" Anyway!
Born Lucky: Dinkleberg, as often referenced by Timmy's jealous Dad
The Cassandra: Crocker about fairies; Wanda about wishes going wrong.
Catch Phrase: When Timmy suddenly discovers something useful that helps him in a given situation, he'll use the phrase "Thank you, [concept responsible for whatever helped him]." For example, when he realizes he can escape a gerbil cage he's locked in (episode entitled "That's Life!") because he has thumbs, he quips, "Thank you, evolution!"
Comic Book Time: None of the characters ever age in the show. Timmy has even had several birthdays throughout the show yet he remains 10 years old. This was cleverly explained in the movie Timmy's Secret Wish, where said secret wish was that everyone would stay the same age forever so that he could keep his godparents. As it turns out, everyone had stayed the same age for FIFTY YEARS.
Compressed Vice: Many characters display traits or flaws that they will otherwise never suffer from in subsequent episodes. Some of these character flaws have taken off in fanfiction and other medium, while others are used as ammunition in shipping wars.
The inclusion of Poof as a main cast member has brought up some confusion regarding his absense in the finale of the movie Channel Chasers.
Also, the addition of Sparky brings on more continuity issues, such as Sparky not being there on the end of Channel Chasers (the same contradiction happened with Poof) and he not being on the live-action movies - A Fairly Odd Movie and A Fairly Odd Christmas - both taking place thirteen years after the events of the main series. In A Fairly Odd Movie, there is even a scene in which Wanda states that Timmy doesn't have a dog.
Contrived Clumsiness: The "accidental" spill variant gets used by Icky Vicky the babysitter. She doesn't just spill a drink, though. It is a significant amount of water, enough to drench the other girl.
Cool Hat: Doug Dimmadome has a cowboy hat that, in at least one episode, always extends past the screen.
Cowboy Episode: Timmy Turner goes back in time to the founding of the city of Dimmsdale. As Dimmsdale is in southeastern California and the city was founded in the mid-19th century, Dimmsdale is depicted as a Wild West town.
Timmy and Jimmy do this in Jimmy Timmy Power Hour 3. They wanted someone to fight together who could be a challenge. They then play the trope straight when they get bored of him and try to ditch him. He gets mad. The reason was because Jimmy told Timmy to make him 'adoptable' whenever they got bored of him. Unfortunately, Timmy types 'adaptable' meaning it ADAPTS to the situation.
Also happens in "The Masked Magician". Timmy causes Mr. Bickles to become a supervillain. When he apologizes, Bickles reforms, but the Vegas act he gets tickes off Britney Britney and she becomes his supervillain.
Criminal Doppelgänger: Timmy Turner's real parents were once arrested during a trip to Niagara Falls by cops who confused them with an Outlaw Couple known as "The Souvenir Bandits."
Cyberspace: Three times: an episode where Timmy wishes for an ultra realistic video game, and an episode where he tries to stop a forged love letter email from reaching its destination, and once in "Channel Chasers" wherein he and Vicky use magical remotes to modify television.
Furthermore, when Jimmy Neutron crosses over, he assumes Fairy World is one of these, as he thinks Timmy's fairies are sentient holograms.