John Belushi was originally cast in the role of Vic and Dan Aykroyd in the role of Earl. The two decided to switch roles just prior to filming the movie. As such, Belushi and Aykroyd starred in this movie acting against type, loud-mouthed Belushi played a quiet character whilst the meeker Aykroyd played an over-the-top character.
Dan Aykroyd wears a pair of sky blue contact lenses throughout the film that have the disquieting effect of making his pupils appear dilated all the time. In the theatrical release and earlier copies of the film this effect is not nearly as noticeable as on HD televisions today.
According to Dan Aykroyd, most of the film's production crew was on cocaine throughout filming, with the inevitable result that John Belushi was sucked back into an addiction he had been trying to quit. Belushi had been completely clean and sober during the making of "Deux drôles d'oiseaux (1981)" which he shot just before "Les voisins (1981)."
Taglines for this movie described it as "A Comic Nightmare", nightmare being an appropriate word to describe this film's shoot. This was a troubled production because the two lead actors argued with the director, the director argued with the producers and everybody tried to rewrite the screenplay. Though the script is credited to Larry Gelbart, much of it was re-written, and Gelbart publicly aired his disapproval. At one point, John Belushi, who would die from a drug overdose within four months of the film's debut, accused writer Larry Gelbart of drinking too much. Belushi's drug use also caused problems for the production of the film.
John Belushi got so sick of John G. Avildsen's directing style that he called his friend and director John Landis late one night and asked if he could take over the movie. When Landis heard they were already filming, he explained that he couldn't do it, due to Landis directing "Le Loup-garou de Londres (1981)." Belushi wanted either Dan Aykroyd, Landis or himself to direct the film. Belushi also allegedly attempted to have Avildsen removed.