JKR's sense of humor

[Carol]

I picked up HBP the other day and started rereading the first few chapters. It's my favorite book of the series despite the events at the end, and, after all, the movie is coming up in mid-July.

I found myself laughing at a particular sentence that I've found funny before. The Muggle Prime Minister (in a skilfully handled flashback) has just heard the frog-faced little man in the painting announce that the Minister of Magic is about to arrive, so "[n]aturally, he had thought that the long campaign and the strain of the election had caused him to go mad" (HBP Am. ed. 3).

Is it just me, or does anyone else find this sentence funny? And, if so, why? I *think* it's the unexpected twist at the end and the deadpan tone in which the line is delivered. But does that qualify as "understated British humor"? It seems more like hyperbole to me--but very subtle hyperbole (in contrast to the descriptions of Hagrid or Dudley, in which the exaggeration is obvious.)

Anyone care to comment on JKR's sense of humor and why a particular example is (or isn't) funny in your view? I'm not talking about crude juvenile humor like Ron's "Uranus" puns, which are obviously geared to preadolescent or early adolescent boys. I'm talking about humor that appeals to adult readers like us--not just the sexual innuendos or the puns, but anything that isn't broad, slapstick, obvious humor.

I realize that humor is subjective and that not everyone shares JKR's sense of humor, but some lines are laugh-out-loud funny. (One that I remember offhand is Fred in GoF addressing Percy as "Weatherby." I don't know why I found that funny. Maybe it was the element of surprise. It seems to me that many of JKR's funniest lines hit the reader with something unexpected at the end. Quite possibly, they're not funny out of context (like the one about the Prime Minister "naturally" thinking that he'd gone mad. And I'm not sure that they qualify as understated humor,  which (as I understand it) takes something dire or drastic or disastrous (like real madness) and treats it in a trivial way. Or maybe I have the concept all wrong.

Carol, suspecting that her own sense of humor is idiosyncratic and inexplicable