The award, created by The Literary Review Magazine, goes to the most "redundant or embarrassing description of the sexual act in modern novels".
Thomas, 37, from London, beat six other nominees to be handed his title by Rolling Stone Mick Jagger at an event at London's In and Out Club.
Thomas said his portrayal of sex was meant to be "provocative, funny and totally outrageous".
An extract from his novel reads: "It is time, time. Now. Yes. She is so small and compact and yet she has all the necessary features.
"Shall I compare thee to a Sony Walkman, thou art more compact and more. She is his own Toshiba, his dinky little JVC, his sweet Aiwa."
The Literary Review started the Bad Sex Awards seven years ago. Past winners include Lord Bragg, Sebastian Faulks, AA Gill and Nicholas Royle.
The original aim was to deter "inept, embarrassing and unnecessary" sexually descriptive passages in books.
However, judging by Thomas's efforts and the calibre of some of this year's other nominees, the magazine may be having trouble getting its message through.
'Lissome limbs'
Among Thomas's rivals was Brian O'Doherty for a passage in his Booker-Prize nominated The Deposition of Father McGreevy.
It features a description of a man's encounter with a sheep.
Edward St Aubyn's A Clue To The Exit describes a woman "bursting like a thermometer".
Another nominee was Candida Clark for a passage in The Constant Eye, while John Updike was included for a passage in Gertrude And Claudius.
Howard Hodgson was also in competition for Six Feet Under along with Wendy Perriam for Lying and Wendy Holden for Bad Heir Day.
Two years ago TV gardener Alan Titchmarsh complained about winning the award for his novel Mr MacGregor, in which he described a man becoming "entangled in the lissome limbs of this human boa constrictor", referring to a female partner.
Thomas seemed more resigned to his triumph and acknowledged that the award could lead to more sales.
But he added, in an interview with The Times: "This is a serious book about male identity and sexuality."