“The dislocation of sex-instinct is one of the chief symptoms of the Fall... The devil is endlessly ingenious, and sex is his favorite subject."1
From the author of the The Lord of the Rings series in a letter written to his son Michael. I think there are other subjects which could be counted among the devil's favorites like pride, love of money, idolatry, etc. But I would affirm that sex is indeed ONE of his favorite subjects. Prudent Christian living involves being aware of the devil's schemes (2 Corinthians 2:11; Ephesian 6:11).
1. I don't have a copy of Tolkien's letters. I just saw it cited in R. Albert Mohler's book Desire and Deceit: The Real Cost of Sexual Tolerance.