Toole only has 2 books published, having never published before his suicide. CoD only made it to light because his mother found the manuscripts and was persistent in getting it out to the world.
The title comes from a Jonathan Swift quote: "When a true genius appears in the world, you may know him by this sign, that the dunces are all in confederacy against him." Ironically, the main character, Ignatius Reilly, considers himself the true genius and everyone who opposes him as the dunces. In reality, while Ignatius may be intelligent, he's so socially backward and egocentric and, well, loathsome, that you feel sorry for anyone who has to come into contact with him.
Initially, Ignatius is taken care of hand and foot by his long suffering mother. He's 30, morbidly obese (his hands are frequently referred to as paws), doesn't work and stays locked in his room watching TV or writing in his Big Chief tablets. At the beginning of the novel, Ignatius almost gets arrested by the police for being a shady character (in New Orleans, this must mean a lot of arrests) but really was just 'studying the crowd of people for signs of bad taste'. He and his mother then get in a minor car accident in which his mom, Irene, has to pay for the property damage. She finds her backbone and demands that Ignatius get a job and help out. And from there it really is as the cover blurb says "marvelous, madcap adventures in New Orleans".
The majority, if not all, of the characters in this book are annoying. But Ignatius is the one who would irritate the Dalai Lama. He's delusional, an incredibly self-involved liar who will do anything to get out of work. It's also quite possible that he's gay, with the hateful mockery of anything sexual, his very very strange masturbation .... uh, techniques, and his plan to have a political party made up of only homosexuals.
Dunces does have a great background in New Orleans and Toole's ability to capture the dialects are really a thing of beauty. Apparently there is a statue of Reilly on Canal Street. I'm sad to say I missed that when I was there but will go look for it when I go back.