Brittany Tenelli is a supporting character in the franchise.
Brittany is a very pretty girl with greyish-blue eyes with reddish pink eyeshadow and blonde hair that is worn in two long pigtail braids held together by four pink holders on both sides. She wears a white and pink camisole that reveals her midriff and belly button, a pink short-sleeved cardigan, pink sweatpants, and pink Mary Jane shoes with white socks. In Jimmy Neutron: Boy Genius, she wore silver and gold bracelets on each wrist, one of each color on each wrist.
Brittany is a very kind, cute, ditsy, clumsy, bubbly, bouncy, innocent, and perky girl. This makes her a ridiculous foil to the brainy Cindy Vortex and sassy Libby Folfax. She is very happy-go-lucky, and with her head in the clouds, she's often confused in a situation. She is an Italian-American friend of Cindy and Libby, who is also a backup dancer with them. Most of the time, she appears as a background character but occasionally hangs around with Cindy and Libby.
- "They're just little puff balls!" - Attack of the Twonkies
- "What'll it be, boys?" - Jimmy Neutron: Boy Genius
- "Uh, I didn't do it!" - See Jimmy Run
- "Oh, my Gosh! Those gems are so gorgeous!" - A Beautiful Mine
- "Excellent choice!" - Jimmy Neutron: Boy Genius
- Brittany is often seen singing, dancing and hanging out with Cindy Vortex and Libby Folfax as a third member of their circle of friends in many episodes.
- Brittany seems to be a parody of Britney Spears due to her name, having blonde hair, her liking to dance and sing, speaks with a valley girl accent and wears midriff-revealing outfits (particularly in her "Baby One More Time" music video).
- Aside from being one of Cindy and Libby's best friends, Brittany seems to be close friends with Amber as well.
- In the film, when the kids are reunited with their grown-ups, Brittany is seen speaking to an old woman and two adults, most likely her grandmother and her parents.
- She made a cameo in Jimmy Timmy Power Hour 2: When Nerds Collide!
- Brittany's pigtails change position depending on her mood.
Minor and One-Shot Characters: Ultra Lord | April the Gorlock | Captain Betty | Commander Baker | Corky Shimatzu | General Abercrombie | Flippy | Jet Fusion | Amanda Neutron | Kari Neutron | Anabelle Neutron | Gomer Neutron | Granny Neutron | Newt Neutron | VOX | Ebenezer Wheezer | Martha Wheezer |