For those who like to say that Chesterton never made an enemy, there is the fact of Thomas Hardy's very last literary work. In the final days before his death in 1928, Hardy dictated what biographer Robert Gittings, in Thomas Hardy’s Later Years describes as "two virulent, inept, and unworthy satirical jingles" directed at Chesterton and George Moore—Hardy's "two most hated critics."
Aleister Crowley, likewise, is fairly characterized as an enemy. According to Joseph Pearce, “It is likely that Chesterton saw in Crowley a vision of the diabolist acquaintance of his student days at the Slade who ‘had a horrible fairness of the intellect that made me despair of his soul’; who sought to ‘find in evil a life of its own’; who sought to corrupt women for no other reason than ‘the expanding pleasure of ruin.”
Now, Crowley was a sexually perverted, black-magic invoking, drug-using Satanist. Pearce: “He liked to be known as ‘the great beast’ and ‘the wickedest man alive.’ It’s difficult to know what this says about GKC’s other enemy, Mr. Hardy, but it cannot bode well for him.