Humour

So Vonnegut, you think you're funny? Well, I think so too, therefore we're in the same boat. At some point in the novel, I forgot all about Billy Pilgrim's unfortunate string of events thanks to the humour you accompany him with. Honestly, who puts time travel into a book about a guy caught up in a war? The combination may seem awkward and unfitting, but to me, that's exactly why it's funny. You don't see any Powerpuff Girls appearing in any Pokemon episodes, now do we? But if it did happen, it'd be quite the hilarious situation. The strange mix of science fiction along with your "true" tale of what happened creates a more light-hearted situation which distracts from the sad, melancholic Billy Pilgrim.
One thing that does bother me is the "so it goes" that accompanies all the deaths mentioned. To me, that isn't really funny, though I'll admit the part where you mentioned the "dead" champagne was clever and made me chuckle. Another thing I find funny about your work are the characters around Billy Pilgrim when he gets captured by the Germans. This may sound mean, but I find the way that the others treat him as funny. In the boxcar when Billy is trying to sleep, no one wants him around since he kicks and yells. A few people respond one after another, telling Billy "Not with me." This leads him to sleep standing up, which if one envisions, looks quite funny. You can't forget when Roland Weary dies. And you better not forget who killed him too- Billy Pilgrim. Everyone knows it, he's the culprit. What's funnier than blaming someone for your death and making sure no one forgets? In my opinion, not much.