From Vonnegut's book "A Man Without A Country":

We had a memorial services for Isaac a few years back, and at one point I said, "Isaac is up in Heaven now." It was the funniest thing I could have said to a group of Humanists. I rolled them in the aisles. It was several minutes before order could be restored. And if I should ever die, God forbid, I hope you will say, "Kurt is up in Heaven now." That’s my favorite joke.