Back Door Sluts 9 is a pornographic film appearing as the focus of the Season Six episode, "The Return of the Fellowship of the Ring to the Two Towers". It is purported to be the "single most vile, twisted, dark piece of porn ever produced" and is cited to make "Crotch Capers 3 look like Naughty Nurses 2".
In "The Return of the Fellowship of the Ring to the Two Towers", Randy Marsh rents both Back Door Sluts 9 and Lord of the Rings. In an effort to loan Lord of the Rings to Stephen and Linda Stotch, Randy accidentally loans them the pornographic film instead.
After Butters Stotch views the film, his behavior, and attitude changes; he emulates Gollum from the Lord of the Rings franchise. The boys retrieve the tape and discuss with their friends what to do with it. Unable to understand why the tape causes aberrant behavior, the group allows Token Black to view it.
Token returns in a catatonic state and declines further participation. The boys, Craig Tucker, Jimmy Valmer, and a kindergartner are later elected to embark on a quest to return the film to Two Towers Video Store in Conifer. During their journey, they are pursued by the 6th Graders.
Once at the store, the film and Butters Stotch are deposited in the dropbox and the group is intercepted by their parents and the 6th Graders. The parents, not knowing that the boys have not seen the film, explain and attempt to make them understand the content of the film.