The Gross Sisters are three bullying sisters who go out in public demanding kids from school and anyone else unable to handle them for their cash, and show violent tendencies. Their parents make them work on the weekends. Their mother is Jamaican; she wears orange flower print clothes and her hair in dreadlocks with a barrette. The remainder of family is entirely blue, including their clothes (except the sisters, who wear black overalls). The reason why is because their family can't afford lotion and they work in the hot sun all day.
Nubia is the middle child and the leader of the pack, considering she is the only one who can talk. Nubia is very reliant on her sisters to do her dirty work and collect the money for her, even though she treats them like garbage. Despite the abuse, Nubia is shown to secretly care for her parents and her sisters, but would never show it or admit it.
Gina is the oldest, despite being the smallest. She is mostly a mute girl. Gina collects money from her sister’s muggings; as a habit, she always has her hand out, even when both hands are required to do something.
Olei is the youngest, biggest, and least intelligent of the three sisters, as well as the most oppressed. Like Gina, Olei is silent most of the time. In the episode, "The Makeover", Olei got separated from her sisters and had to decide on whether to go back to hanging out with them or still hang out with Penny. For continuity's sake, she goes back to her sisters, but secretly shows that she and Penny are still friends. This shows that Olei could be nice and sweet, if her sisters weren't so mean to her all the time. It is also implied that Olei might have romantic feelings for Penny.
Although they rarely get in trouble for their deeds, they do get caught in one episode. They are usually friends with Penny, but sometimes they bully her and her friends. After witnessing Penny fighting the Carver clone on national TV, they develop respect for her with Nubia calling Penny "hardcore". Their catchphrase is "Hands up. Cash out".
- "Suga Mama's Believers"
- "It Takes a Thief"
- "Bring It On"
- "Spelling Bee"
- "She's Got Game"
- "The Party"
- "I Love You Penny Proud"
- "Puff's Magic Adventure"
- "Enter the Bullies"
- "The Altos"
- "Romeo Must Wed"
- "A Hero for Halloween"
- "Poetic Justice"
- "Pulp Boot Camp"
- "Tween Town"
- "Adventures in Bebe Sitting"
- "Surf and Turf"
- "Twins to Tweens"
- "Culture Shock"
- "Who You Callin' a Sissy"
- "Psycho Duck"
- The Gross Sisters are bullies similar of a mix between the fifth graders and the Ashleys from Recess and the Trix from Winx Club.
- The Gross Sisters are similar to the Greasers from CatDog and the Kanker Sisters from Ed, Edd n Eddy, as all three trios usually get away with their crimes.
- They're similar to the Trix from Winx Club, because they act a similar way to them and are sisters and antagonists.
- The Gross Sisters may do some bad things, but they are more like anti-heroes than total monsters.
- According to Penny, Olei doesn't talk because she's shy. It is unknown if this is true or if Olei and Gina are actually mute characters.
- Their first names are a play of skin care products Olay, Neutrogena, and Nivea.
- Ironically, they have ashy and dry complexions.
- Nubia once dated Wizard Kelly's son.
- Penny briefly became one of the Gross Sisters, but they kicked her out when Nubia realized that the fact that Penny was sent to boot camp makes her a real criminal instead of a bully.