Carl likes to eat, and this caused him to be overweight. When his parents expanded their cable line-up, Carl found himself focusing on a channel devoted to llamas and a show about a superhero called Llama Boy the Super Hero. He has adored llamas ever since, going so far as to join a fan club, the Llama Love Society (which he likely created, since he is shown to be the only member). He even turned into a llama once. He is allergic to almost everything, and has asthma. Carl often unknowingly gives Jimmy his brilliant ideas.

[the aliens are making the parents do a chicken dance]
Nick: They're making our parents dance so lame.
Carl: No, my dad really dances like that.

Jimmy: What girl wants to dance with a guy who looks like he should still be in Gymboree?
Carl: [quietly] I didn't think we liked girls yet, Jim.
Jimmy: Oh, we don't, we don't, no, not yet. However, one day, Carl, an influx of hormones that we can't control will overpower our better judgment and drive us to pursue the female species against our will.

Carl: Hey, this astronaut food isn't too bad.
Jimmy: That's toothpaste, Carl.
Carl: Oh. Minty.

"Ok, I'll have one more and then that'll be it." - Jimmy Neutron: Boy Genius
"Um, yes, are you going to finish that croissant?" - Lights! Camera! Danger!
"Time to take out the trash!" - Sleepless in Retroville, Attack of the Twonkies
"OUCH! Sheen, that hurt!" -Broadcast Blues
"Ow, my scapula!" - Carl's catchphrase
"Llama, llama, llama!" -Jimmy Neutron: Boy Genius
"I don't know, Jimmy..." (Usually when testing one of Jimmy's inventions)
"Saying goodbye to your kids is always painful, Jimmy." - Who's Your Mommy
"It's a good thing my underwear was clean." -King of Mars
"Guys, can I have my pants back?" -King of Mars
"But why did you wink? Why'd you gimme a dollar?! My brain hurts!!!" -Jimmy for President
"Jimmy Neutron, he's a spy! He's a kid and his hair is really high! He's got a friend named Carl who is really cool. And a friend named Sheen ... WHO WAS HELD BACK FROM SCHOO-OOL!" -Operation: Rescue Jet Fusion
"Thanks. I saw that in a soap opera once..." -Raise the Oozy Scab
"Who's eating whom??" -Stranded
"Flying metal chicken..." -The Eggpire Strikes Back
"I want my mommy!!!! ...And some fudge." -Hall Monster
"So?? Pinching still hurts!" -Normal Boy
"Thanks, guys! I thought I was gonna be snake food!" -Beach Party Mummy
"Aw, c'mon, guys. Eighth place isn't so bad..." -Battle of the Band
"RUBY MADNESS! RUBY MADNESS!" -A Beautiful Mine
"Jimmy, why is it so unseasonably humid?" -Sorry, Wrong Era
"Will you be my mommy?" -Operation: Rescue Jet Fusion
"I'm a bad Watson!"-Crime Sheen Investigation
"Uh, I want sour. No! Uh, salty. No! I don't know which one to choose!" - Krunch Time
"HELLO, RETROVILLE! I hope you had a scrumpdillyicious day! Let's wish a big old happy birthday to old lady Nusbaum who turns 102 today! Here's a nice big weather center hug from Dr. Carl!" - Lady Sings the News