- The infamous 200th issue, especially when you look at it from the perspective of Carol Danvers. She suddenly becomes pregnant, without any memories of having sex at all, and then ends up giving birth within a few days. Then her "son" rapidly ages into a grown man, who reveals that he had used super-science to abduct her between dimensions, "assist" her in falling in love with him, then impregnated her with a clone-avatar of himself in an effort to try and break free of his own dimension, using those same mind-altering machines to wipe her memory of the entire affair. Then, when forced to return, he triggers her subliminal programming and compels her to come along with him. And all the while, her "friends" in the Avengers stand by and do nothing, completely ignoring both her initial panic and concern over the pregnancy and then her obviously unnatural change in behavior. This one horrified readers and writers so much that, a year later, Chris Claremont canonized the fact that Danvers was raped by having her chew out the Avengers over it.
- The "Under Siege" storyline had Zemo trying to break Captain America by destroying his mementos and torturing his friends, letting the savage Mr. Hyde loose on Jarvis. What happens is entirely off-panel, but the sound effects, dialogue, and expressions say it all.Black Knight: How could any man do such a thing... and laugh?
- Being replaced by a Skrull. You can come back years later and everything you know has changed. Your friends and people you have dated might be dead. The Skrulls don't just steal someone's image, they steal their entire lives, sometimes ruining them in the process.
- Mockingbird and Spider-Woman's experience are particularly terrifying because, not only was Mockingbird gone for three years, she was hunted by Skrulls after she saw through their tricks, with one of them impersonating Clint while he hunted her. She eventually snapped and killed him. Spider-Woman came back to discover that nobody trusted her after Veranke used her face.
- The experience of Hank Pym (Ant-Man 1) isn't much happier; he returns to find out that his Skrull doppelganger seduced and impregnated Tigra, a fellow Avenger he'd actually had a crush on. Fortunately, Marvel decided to throw him a bone after years of abusing him over that one time he accidentally smacked Janet and instead things ended up working out nicely, but still, that's really a horrifying scenario in so many ways...
Nightmare Fuel / The Avengers