Mailer, who died of renal failure last month at 84, was one of several candidates for the annual "Bad Sex in Fiction Award," which aims to highlight crude and tasteless descriptions of sex in modern novels.
In a ceremony at the In & Out Club in central London, the judges paid homage to a "great American man of letters," adding: "We are sure that he would have taken the prize in good humour."
The excerpt is taken from one of Mailer's last works, "The Castle in the Forest," a fictionalized exploration of Hitler's family, narrated by a demon. In the passage, the demon describes the moment Adolf is conceived, as Klara Hitler embraces her husband Alois, a man the novel says was also her uncle, "with an avidity that could come only from the Evil One."
That passage, and others like it, were chosen by the Literary Review magazine, which has been embarrassing authors with the award for the past 15 years.
Those shortlisted for this year's prize included Christopher Rush, whose book "Will" offers a firsthand account of sex between William Shakespeare and his wife, Anne Hathaway. The bard praises his wife's anatomy in excruciating detail.
Jeannette Winterson was picked for her awkward love scene in "The Stone Gods," involving a woman and a robot. Richard Milward's "Apples" was chosen for its description of a sex scene between an adolescent boy and a woman the teen said "smelt a bit like an armpit."
Actor David Thewlis, who appears in the Harry Potter movies as Harry's teacher Remus Lupin, was selected for a sex scene in his novel "The Late Hector Kipling," where a man has his nipple drenched in lighter fluid, set on fire, and then doused in beer.
Earlier this year Thewlis was nominated for a "Razzie" - a prize handed out for awfulness in show business - for worst supporting actor in both "The Omen" and "Basic Instinct 2: Risk Addiction."