Slapstick (subtitled "Lonesome No More") as well as describing the strange childhood of the Swain twins, also paints a picture of a post apocalyptic world, where new York has been destroyed, and people are camping out in the ground floor of the abandoned Empire State Building.
The damaged male twin has managed to become the last president of the USA with a campaign built on the slogan "Lonesome No More", offering everybody the chance to join new extended families by the addition of new middle names.
The book is another of Kurt's attempts (IMHO) to describe the loneliness and futility of existence, but also that that life has an ironic humorous side. Whilst not dealing with the same big issues as Slaughterhouse 5, it speaks to me of much that is flawed but admirable in the human spirit- and it's bloody funny.