A Conferderacy of Dunces is a Pulitzer Prize winning novel that is hysterical. Toole (the author) wrote the book and then died an umtimely death to suicide. Years later, his Mother presented the manuscript she found to a publisher and the rest is history.
Ignatius J Reilly is the central character - a fat slob with a complex personality disorder. The story is set in New Orleans and you follow Ignatius (who is grown and living with his Mother) on his shenanigans through the city as he just tries to get by doing as little as possible. The book is hysterically funny at many points, but sad at other junctures. It is overtly crass at times and may not be suitable for young children (should at least be screened by parents before being read by pre-teens and teens).
Definitely worth the time, this is a masterpiece.