Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Creepshow
The end of They're Creeping Up on You! is perhaps the only genuinely frightening thing in the film (most everything else is deliberately silly) but it's absolutely horrifying. Also an example of Nausea Fuel and Paranoia Fuel.
Also, Richard's revenge. Being immobilized in sand while the tide gets closer and closer to you and ultimately covers you.
Harry threatening Richard is more scary in that sense too. Especially when he manages go through with it after his death.
THAT THING, in an otherwise mostly-innocent anthology horror movie. Hint: box
Well, if it's some consolation, there's a lot of real cockroaches, but also a lot of dead cockroaches and a lot of brown cockroach-shaped stuff to bulk out the mass.
Tom Savini (who has a massive bug phobia) mentioned in a book on effects that when one of the cockroaches touched him, he teleported across the room. Not really a joke - he has no memory of physically crossing the room.