Big "NO!": In The Tomorrow Boys, after learning he gets married to Cindy. In a bit of Leaning on the Fourth Wall, the scream cuts to a commercial. When the show comes back on, Sheen comments that he had been screaming for four minutes straight.
Brilliant, but Lazy: Why do something as simple as neatly put away your piles of pants when you can implant chips in them that do it for you? Carl and Sheen call him out on this, though.
Cassandra Truth: In the episode, "The Eggpire Strikes Back", no one believes Jimmy when he says that the Yolkians, the villains from the pilot film, are still just as evil as ever.
Catch Phrase: Originally "Gotta blast!" "Think, think, THINK!" and "Brain blast!". The show eased off on these as it went on, eventually getting rid of them entirely. (One exception is "And now, my latest invention, the (insert plot-related-device here!)", which stayed for most of the series' run.)
Crazy-Prepared: His watch, whose powers depend mainly on the plot. Can include lasers, freeze rays, magno-rays, GPS, tracking devices…you name it, there's probably a gadget for it tucked away in there.
Sheen: Fascinating! Can you make it do the hokey pokey?
Jimmy: Sheen, go home.
Fatal Flaw: Jimmy's greatest flaws are a combo of Pride and his lack of common sense; in fact, many of the conflicts in the show are born out of this.
Future Loser: In the 'Bad Future' of The Tomorrow Boys, Future!Jimmy is a slack-jawed loser, wanted by the evil dictator Libby, with a five-o'clock shadow and Cindy as a wife. Current!Jimmy is less than impressed.
He Cleans Up Nicely: When Jimmy shows up in a tux for Jet Fusion's wedding to Beautiful Gorgeous in My Big Fat Spy Wedding, Cindy promptly gets little hearts in her eyes.
Cindy: "So Neutron's the best man? Yeah, more like the best NERD! I bet he'll look like a total…" (Jimmy shows up outside the church in a tux. Cue fade to pink background, eye-hearts and hair patting) "…HUNKMUFFIN."
Another example is during Love Potion #976-J, when Jimmy cleans up for his date with Cindy. Said almost word-for-word by Cindy.
"Hell Yes" Moment: Often. Especially when he's given up all hope…and then his friends forgive him for being arrogant/apologize for being stupid/come back to save him.
Pet's Homage Name: Jimmy designed and built his robot dog and named him Goddard in honor of rocket science physicist and inventor Robert Goddard. Especially apt when, in his first animated feature film, Jimmy is able to ride upon Goddard like a space bike.
Gasshole: He has burped more than anyone else on the show (except for Jimmy's dad). In "The N-Men", he takes a Super Serum that turns him into "Belch Boy", allowing him to unleash sonic blast burps by drinking seltzer or shaking himself really hard.
Jimmy's hyperactive other best friend who is obsessed with the comic book superhero Ultra Lord.
Accent Adaptation. In the Latin American dub, he speaks with a Japanese accent, possibly because the translators thought that he's Japanese-American, instead of Hispanic, and his name should be pronounced "Shin".
Fartillery: Gets this when she ate the Belch Boy packet in "The League of Villains" and proves to be better at it than Carl, given that she doesn't need seltzer or to be shaken to burp, and she can eventually control her burping to do it at will.
Gasshole: Becomes one after eating the Belch Boy packet in "The League of Villains", even to the point of making a dance out of her burps.
Satellite Character: Was originally one for Cindy, and several of her earliest appearances had her personality as more or less an echo of Cindy's, but as the characters got more development, she became more distinct.
Shipper on Deck: She's FOREVER pleading with Cindy to just tell Jimmy how she feels and get it over with!
Ditzy Genius: Not ditz per se (she's certainly the intelligent one in her marriage with Hugh and more rational than he is) but she has her moments of ditziness. There are also numerous moments where she demonstrates it's definitely from her side of the gene pool that Jimmy gained his intellect.
Demoted to Extra: Earlier episodes were building him up to be an important character. Then he vanished.
Paper Tiger: He's the ultimate cool dude, the girls all dig him, and he's supposed to be tough. In the movie, his part of the plan is to take care of the Big Bad while the others rescue their parents. One look at his competition, though, and he goes screaming like a little girl.
Jerkass: N-Men episode again. Granted something should have been done to try to help the kids control their new found powers. However, calling the military up to imprison them and then telling the kid's parents they were just freaks?
Verbal Tic: Has a habit of ending his sentences with, "Yeah!".
Doing in the Wizard : His seemingly supernatural hold over reality, time and space is actually caused by a pair of matrix generators hidden in his cuff links.
Faux Affably Evil: Rarely drops his cheery, hammy attitude even while threatening to blow up people's planets. At the end, he finally stops and decides to get serious.
Hypocrite: Insists during the race that there's no cheating allowed, but permits the Brains to put Jimmy and the gang into a Lotus-Eater Machine. Later he panics at the idea of his quadrant being blown up despite the fact that his entire show is about blowing up comepletely innocent planets simply because their species lost a game.
Karma Houdini: The worst he gets is being forced to hand over his show to the Brain aliens and advertise an exercise machine that implements Electric Torture. Probably justified as he's implied to be indestructible.