Ironic and absurd
In my opinion, ironic and absurd are the adjective that characterize Vonnegut’s tone. Infact his novel’s black humor is built in a way to get to the absurd when, for example, he refers to the prisoners that in his point of view are similar to animals as “meat locker”.
Otherwise the dialogue of Wild Bob is a clear example of the second one, he lost his soldiers in the battle. He had assured them that are many Germans dead that are praying God not to meet him and his soldiers, his words are a clear moment of absurdity when we realized that he lost his mind.