This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Strangers
You should never invite these people to your home.
In case you didn't already realize it, Joanna Newsom's "Sprout and the Bean" is terrifying (especially on vinyl, especially when it skips). As an added bonus, at first it seems like a cute children's song with bizarrely unnerving music, and is creepy enough... until you pay attention to the lyrics and you realize that it's probably just as disturbing as the movie.
The use of My First Lover by Gillian Welch is even more so, with the loop adding to the air of insanity and chaos. The atmophere is so effective the same looping section of the song was later used in the youtube horror short No Through Road.
The most unsettling part of the film is the reason the Strangers tormented the couple. Why did they psychologically torment them and then finally plan to kill them? Because they were home. Never once does Truth in Television fit here so hard.
Worse, unlike most movies in the horror genre, The Strangers is completely devoid of comedic features (not even a single gag), which is quite rare when even the darkest horror movies have had their comedic moments.
The only scene in the film that could even be considered slightly funny is halfway through, when Kristen is hiding in a closet near the kitchen. The Masked Man enters the room, and sits down at the table, apparently taking a break. Though it's a very tense scene, it might elicit a small nervous chuckle at the idea of this psychopath taking a break. A moment later, he gets up and leaves the room...but not before turning and staring directly at the closet; he knew Kristen was there the entire time.