They are bullies that go out in public demanding people 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. Gina is the oldest, despite being the smallest. She collects money from her sisters' muggings; as a habit, she always has her hand out. Olei is the youngest and the biggest of the 3 sisters. Like Gina, Olei is silent most of the time. In the episode, "The Makeover", Olei (who is known as the "muscle of the group") is separated from her sisters and is faced 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.
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"
- "Boot Camp"
- "Tween Town"
- "Adventures in BeBe-Sitting"
- "Surf and Turf"
- "Twins to Tweens"
- "Culture Shoc"
- "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.