Brittany Tenelli is a supporting character in the franchise. She is an Italian-American friend of Cindy and Libby, who is also a backup dancer with them. She usually appears as a background character but occasionally hangs around with Cindy and Libby. She is voiced by Candi Milo.
Brittany is a very pretty girl with grayish-blue eyes with red-pink eye-shadow and blonde hair that is worn in two long pigtail braids held together by four pink holders on both sides. She wears a midriff-baring white and pink shirt, exposing her belly and belly button, a pink short-sleeve jacket, pink pants with white and pink waistbands, and pink Mary Jane shoes with white socks. In Jimmy Neutron: Boy Genius, she wore gold and white bracelets on both of her arms, one of each color on each arm.
Brittany is a very kind, sweet, ditsy, clumsy, bubbly, bouncy, innocent, and perky girl. This makes her a comic foil to the brainy Cindy Vortex and Libby Folfax. She is very happy-go-lucky, and with her head in the clouds, she's often confused in a situation. Brittany sometimes gets picked on by Cindy and Libby when she tries to get involved with their escapades, but they still love Brittany, and the three of them are very close.
- "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 God! 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 outfits (particularly in her "Hit Me 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.
- Brittany has a loud and high-pitched laugh that the characters find annoying.
- In the movie when the kids are reunited with their folks, 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 |