Most readers here seem to believe that this is meant to be a comic novel, which I think is a fundamental misreading. It seems clear to me that Carkeet is presenting us with a case study of Narcissistic Personality Disorder (NPD) and has given us in Jeremy Cook a protagonist so consumed by his pathology that the reader cannot help but feel for him even as they are repulsed by him:
--He overestimates his own importance (considers himself the "resident genius" of his office, even though in a telling episode late in the book, he is bested by a layman concerning the etymology of the word "Hoosier"; expects the local police to keep him apprised of developments in the murder investigation, even though he is neither law enforcement nor really part of the venerable tradition of amateur detectives in fiction, as he does not attempt to find the murderer, only stumbling across a key piece of evidence very late in the novel)
--He constantly demands excessive praise from those around him (to the extent that, poignantly, all his coworkers have clearly learned to pepper their conversations with him with reassurances, telling them that "of course" he is famous in his field, that he is considered attractive, that everyone respects him immensely)
--This is with good reason, since Cook relentlessly examines the speech of others for anything he can perceive as an insult. When he does believe someone has slighted him, his reactions are excessive (when a colleague includes Cook in a statement that in their office there are "no saints", Cook feels "suddenly depressed"; when he overhears what he believes to be a derogatory comment concerning himself, he excuses himself to have what can only be described as a tantrum in the bathroom, and he devotes most of his energy for the rest of the book to tracing the source of this remark)
--He lacks any empathy for those around him and considers himself superior to them, referring to them as morons, bastards, empty-headed, etc. When he attends the funeral of a colleague, his chief concern even when speaking to the widow of the deceased is whether he appeared ridiculous by arriving late.
That this has isolated Cook from those around him seems undeniable: his closest "friend" is a man who cannot stand him, his romantic relationships are short-lived, and he cannot connect with his fellow human beings. He is essentially a terribly lonely man. When Cook refers to "the heavy weight of misery and turmoil" he has experienced during the events of the novel, he refers not to the murder of a colleague (this does not affect him much), but to the constant hell he experiences as a man whose insatiable need for praise has consumed his life and his sanity. Though many people can testify to the unpleasantness of knowing or being in a relationship with a person with NPD, Carkeet reminds us that for the afflicted, the experience is much, much worse.