Complete Monster: Raoul is one of three robbers who invades the new home of a mother and her daughter, and from the start he proves himself to be far more cruel and murderous than both his comrades. He has no reservations about killing people or even children to get the bearer bonds stored in the safe room. He turns up the gas so Meg and Sarah almost suffocate and doesn't care that his associate Junior almost burned to death as a result. When Junior tries to cut his losses and leave, Raoul shoots him in the head, then shoots the corpse again out of spite. He threatens to kill Burnham too if he doesn't go through with the job. He beats Meg's ex-husband Stephen almost to death to get them to leave the safe room, and then intends to kill her daughter if she tells the police. After they beat Raoul up it gets personal, as he prefers to murder the whole family rather than escape with the money.
Hilarious in Hindsight: David Fincher on the DVD commentary complimenting young Kristen Stewart, saying she'd never "have child star issues" and that "she'll probably never end up on E! Entertainment Television." He was basically right about the former, but the latter... in fairness, he couldn't have known about Twilight and Robert Pattinson (not to mention the whole Snow White and the Huntsman thing).
Moral Event Horizon: For some, it's when Raoul murders Junior in cold blood. For others, it's when he beats Stephen to within an inch of his life.
What an Idiot!: Junior has a lot of these, but one stands out, and doubles as a Establishing Character Moment. When he discovers to his chagrin that Meg and Sarah are already in the house, he explains that when the realtors told him how many days it would be before they moved in, he assumed they meant business days.
Hell even Stephen especially when he's beaten to near death by Raoul.
Viewer Gender Confusion: Sarah can easily be mistaken for a boy early in the movie, due to her short haircut, voice and gender-neutral wardrobe, but the confusion is usually cleared up when her name is finally spoken.