Citizen Toxie is full of cameos, including Stan Lee, Corey Feldman, James Gunn and Lemmy. Also, Ron Jeremy plays the mayor (and SCREW Magazine publisher Al Goldstein plays his lackey).
Eli Roth appears in a blink-and-you-miss-it cameo in Toxie.
The Other Darrin: Toxie has been played by a total of five actors across the four films: Mark Torgl (Melvin)/Mitch Cohen (Toxie) in the original, John Altamura (and his stunt double, Ron Fazio) in II and III, and David Mattey in Citizen Toxie.
The Other Marty: John Altamura, the original actor that was hired to play Toxie in the second and third films, was fired halfway through filming due to an alleged case of Small Name, Big Ego. Because they couldn't afford to re-shoot the footage, they just had his stunt double, Ron Fazio play Toxie for the rest of the shoot. In a rare case of this trope being acknowledged, both men were credited as Toxie in the finished films.
Our Lawyers Advised This Trope: An early teaser trailer for Citizen Toxie included Hugh Hefner loudly declaring "Only The Toxic Avenger knows for sure!". Although Troma was given permission to film at the Playboy mansion, Hefner never gave them permission to use the Playboy name nor his likeness, and a cease-and-desist letter caused Hefner to be purged from all subsequent trailers and the film proper.
Too Soon: Awesomely averted. Citizen Toxie was released in the States shortly after the events of September 11th. While most films underwent editing to remove images of the Trade Center, Citizen Toxie didn't. It received a standing ovation from a New York audience for this.
Working Title: The Monster Hero, which is why the line gets thrown around so much in the first movie - it was supposed to be a Title Drop.