This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / American History X
Though not directly seen, the infamous curb stomp will haunt your nightmares long after the credits.
As will the expression on Derek's face as he's being arrested, smiling as if he had done nothing wrong.
A gang of jack-booted, stocking-capped thugs storm your home and trash it while telling you to "go home". They drag your cashier onto the counter and drown her with milk until she's white. If you don't want to become white, they have baseball bats to convince you to try.