This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Veronica Mars
The child abuse episode. The ending where Sheriff Lamb appears to hate it, but also can't do anything about it, almost seems realistic.
"Leave It To Beaver": Veronica gets locked in a refrigerator and then SET ON FIRE by the man who killed her best friend.
"Not Pictured": Cassidy blows up a plane while Veronica can only watch, thinking that her dad's on it (he's not). Then he tries to kill her, fails, and in one of the most heartbreaking moments on the show, he jumps off the roof of a tall building after Logan tries to stop him, but can't actually come up with a reason that he shouldn't jump.
The revelation that Gia and Cobb aren't having a consensual affair; rather, he's been blackmailing her for sex regularly for nine years, and can assume control of her life anytime he feels like it, having taken the apartment opposite hers so he can watch her every move. The last line of her reveal - "I'm not even allowed to have curtains" - is incredibly creepy, not to mention a real Tear Jerker. She was raped for 9 years and then murdered by him the moment she stepped out of line.
Worse given that as this blackmail starts, she's only - at best - JUST getting past the trauma of learning about her father being a child molester. She would have just been in the process of piecing her life together again when she's effectively turned into a sex slave.