This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Shel Silverstein
There was a Shel Silverstein drawing for a poem about a kid wanting a pet monster of a huge lion with an ugly face and gigantic nose.
Also Silverstein, his poem Peanut-Butter Sandwich made some afraid that if they ate peanut butter their mouth would eventually be sealed shut and cause them to starve to death.
In a related note, at least one edition of The Giving Tree devotes its entire back cover to the least flattering photo of Silverstein that could ever be printed. It makes him look like a horrible dwarf that hiked out of the uncanny valley with hopes of joining the circus. This slightly blurry black-and-white photograph takes up the book's ENTIRE back cover.
This was referenced in Diary of a Wimpy Kid, in which the protagonist, Greg, is scared by a similar portrait - which his father uses to make sure he doesn't get up in the middle of the night, saying that Silverstein would be outside.
There's also the back cover◊ of A Light in the Attic. There's something very off about his smile, and how his head is shrouded in all of that blackness...
The one about the monster standing right behind me, coupled with that horrible drawing, related to the poem mentioned above.
The introduction to "Uncle Shelby's A-B-Z Book" pretty much sums it up. Although it must be remembered that Mr. Silverstein will, for some time to come, be associated with the kind of grass that does not grow on lawns. Which goes a long way towards explaining some of his poetry.
"Hungry Mungry". Some normal person eating his family, then the world, then the freaking universe, and then his body, and still being alive to gnash his teeth because there's nothing left to eat...
"Obedient". A kid gets in trouble at school. He has to stand in the corner. They forget to tell him to go home the next day, and the next. He stands there all through summer vacation. They close down the school. He stands there for forty years.
There was always something ...wrong about the cover to Light In The Attic.