This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Six Feet Under
Realistic and disturbing "That's My Dog" is an entire episode of a realistically terrifying carjacking. David picks up a "cute" hitchhiker who forces David at gunpoint to take out all his money at an ATM, beats and punches him, forces him to smoke crack, makes him suck the barrel of a gun, threatens to set him on fire after pouring gasoline on him, steals his van, and leaves him in the middle of nowhere, beaten half to death.
His frequent hallucinations afterwards are horrifying in many different ways.
Lisa's decaying, partially shark-eaten corpse.
Many gruesome deaths that are depicted on screen:
A baker gets hacked into pieces by a dough machine.
One opening teaser scene featured a first person perspective of a three week-old infant lying in a crib. As the adoring parents leave the baby to sleep, the camera (serving as the baby's perspective) looks up at the roof into a rather creepy black and white baby's mobile. As the camera blurs and zooms, the shot fades to white.