This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Animal Kingdom
The beginning of the film. Joshua's mother's death, followed by the arrival of Smurf and the ominous music playing over the opening titles, really set the tone for what follows.
Pope Cody is walking nightmare fuel.
His interactions with Nicky. The scene where he takes an unconscious to bed is unbearably tense and creepy, and Joshua's arrival and diffusion of the situation really does nothing to ease this.
Naturally, his murder of Nicky as well. He suffocates her for basically nothing, while a high, panicked Darren watches on helplessly. Even worse, this probably wouldn't have happened if Darren hadn't told J to dump her.