This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Sleepaway Camp
Admit it. The ending scared you shitless.
The scene where the aunt tells calmly that "Angela will be a lovely name for him" to Peter. Think about it: she's forcing her traumatized nephew into pretending he's his sister just because she already has a son. Bitch needed to DIE.
Judy's horrific death scene. She's held down with a pillow while Angela grasps a hot curling iron before shoving it into (most likely) her vagina. Only the shadows are shown, but you can hear her skin sizzling as the iron is pressed inside.