What's the most revolting TV show, book or movie you've ever seen?S

The flipside of a sense of wonder is often a sense of total disgust and revulsion, when you see just how gross and awful things can be. But which science fiction, fantasy or horror story has grossed you out the most?

Please include a (work-safe) picture or clip of this revolting spectacle. And let us know the title, and why it was so nasty. Thanks!

Top image: Slither (2006).