Derek and Clive Get the Horn (1979)
Derek and Clive Get the Horn is a 1979 British documentary comedy film that chronicles the recording of Peter Cook and Dudley Moore's 1978 comedy album Derek and Clive Ad Nauseam, their third and final outing featuring their controversial alter-egos Derek and Clive, two foul-mouthed lavatory attendants who banter at length about their surreal day-to-day existences. The footage was shot in early September 1978. The film was the directorial debut of Russell Mulcahy, who would go on to direct Highlander.
More at Wikipedia.