Brittany O'Malley (Kelli Garner) is the main villainess of "Mean", episode 5.17 of Law & Order: SVU (airdate February 24, 2004). She was a popular student at Tanner Day Academy and was part of a clique with three other girls at her school: Paige Summerbee, Andrea Kent, and Emily Sullivan (the leader). All four girls were vicious bullies, with Emily's biggest target being outcast Agnes Linsky. In actuality, though, Brittany hated Emily and wanted to get rid of her from the group.
As a test of their friendship, Brittany ordered her actor boyfriend Lukas Ian Croft to start dating Emily. When she later learned that Lukas and Emily were continuing their relationship, Brittany became enraged and poisoned Lukas' cat out of spite. This also led the evil Brittany to kidnap and torture Emily, with Andrea and Paige assisting her. The girls lured Emily out of her house one night before tying her up with duct tape and throwing her in the trunk of the car. After driving for a while, Brittany flew into a rage and began assaulting the bound Emily, beating her up and burning her with cigarettes. The sadistic Brittany then cut Emily with a pair of manicure scissors before finally stabbing her to death with a knife. The girls then left Emily in the trunk and took the train home after going out to eat. When Benson and Stabler questioned the girls, Brittany used Emily's relationship with Lukas to subtly finger him as her killer.
Later on, after Brittany sent photos of Agnes Linsky in the school's locker room to their entire school, she was assaulted by Agnes' vengeful brother Troy, but refused to press charges against him. When Benson confronted her about the pictures, Brittany tearfully claimed that she did so to get back at Agnes for killing Emily. But eventually, the detectives uncovered Brittany's evil crime, bringing in all the girls for questioning. After intense interrogation, Andrea and Paige confessed to what Brittany had done to Emily. When Brittany learned that her friends had turned on her, the psychotic villainess had a breakdown in which she had to be restrained by Captain Cragen. Brittany was arrested for Emily's murder, but received a reduced sentence for testifying against her co-conspirators.