Maniac is a 1980 American slasher film (though considered more of a splatter film), about a disturbed and traumatized serial killer who scalps his victims. It was directed by William Lustig, and co-written by Joe Spinell (who also developed the story and starred as the lead character) and C.A. Rosenberg.
Frank Zito is a middle-aged, overweight man living in an unspecified borough of New York City, possibly The Bronx, Staten Island or Brooklyn. Frank works as the janitor of an apartment building, a detail revealed only through the presence of keys displayed upon a corkboard beside his apartment door. At night, his personality degenerates into that of a mumbling schizophrenic, who carries on one-sided, often incoherent conversations with his dead mother while stalking around a small bedroom filled with hacked-up mannequins and childhood mementos. As the film progresses, the audience becomes privy to Frank's nighttime stalking sessions, in which he ventures into the city to kill and scalp women. Frank then brings their scalps back home to nail to mannequins, which he then sleeps with for several nights before placing the mannequin in another area of his apartment and going out again to repeat the process.
Midway through the film, Frank befriends and then romances a fashion photographer, but his daytime life and nighttime life begin to merge, to the point that he loses his tenuous grip on reality altogether. The film's now infamous ending finds Frank's mannequins transforming into the re-animated corpses of his victims, which then proceed to pin him to his bed, disembowel him, and decapitate him. The next morning, detectives break into Frank's apartment and find Frank dead on his bed of a self-inflicted machete wound. After the detectives leave the room to secure the rest of the apartment, however, Frank's corpse opens its eyes.
Frank's motive, and why exactly he does these things -his "fantasies"- is explained when it is revealed that he was abused by his mother.
The film also has a somewhat notorious ending among horror film fans, as it is not only completely open-ended, but provides a variety of possibilities as to what actually occurred, all of them contradictory.
Despite the attention paid to the climax, however, the film's most infamous and widely talked about scene is the "Disco Boy Scene," in which special effects man Tom Savini, dressed in full 1970s disco regalia, has his head blasted off with a shotgun while making out with a woman in the front seat of a vintage car. The scene -filmed in slow motion and lit entirely by the reflected headlights of the car- is extremely graphic and realistic in its depiction of the damage caused by the man's head being blown apart at near point blank range by 12-gauge buckshot; Savini himself was a Vietnam War veteran, and used his firsthand knowledge of the carnage he saw on the battlefield to create the effect.

Portions of the film can been seen on the DVD release.