I came to this conclusion recently while passing through Customs and Immigration at Logan Airport in Boston. As I approached the last immigration official, he said to me: "Any fruit or vegetables?"
I considered for a moment. "Sure, why not," I said. "I'll have four pounds of potatoes and some mangoes if they're fresh."
Instantly, I could see that I had misjudged my audience and that this was not a man who ached for banter. He looked at me with one of those slow, dark, cerebrally challenged expressions that you never want to see in a uniformed official, but especially in a US Customs and Immigration officer because, believe me, these people have powers you really do not want to put to the test. If I just mention the words "strip search" and "rubber gloves" I think you will latch on to my meaning. When I say they have the legal right to interrupt your passage I mean it in every possible sense.
Luckily, this man appeared to conclude that I was just incredibly thick. "Sir," he enquired more specifically, "are you carrying any items of a fruit or vegetable nature?"
"No, sir, I am not," I answered at once and fed him the most respectful and grovelling look I believe I have ever mustered.
"Then keep moving, please," he said. I left him shaking his head. I'm sure that for the rest of his career he will be telling people about the knucklehead who thought he was a greengrocer.
So take it from me, never joke with an authority in America, and when you fill in your landing card, under the question "Have you ever been a member of the Communist party or employed irony in a public situation?", tick "No".
Irony is, of course, the key word here. Americans don't use it much. (I'm being ironic; they don't use it at all.) In most circumstances this is actually rather a nice thing. Irony is cousin to cynicism, and cynicism is not a virtuous emotion. Americans - not all of them, but a significant proportion - have no need for either one. Their approach to everyday encounters is trusting, straightforward, almost touchingly literal. They don't expect any verbal sleight of hand in conversations, so it tends to throw them when you employ it.
We have a neighbour on whom I tested this hypothesis for the first two years we were here. It began innocently enough. Soon after we moved in, he had a tree come down in his front garden. I passed his house one morning to see that he was cutting the tree into smaller pieces and loading them onto the roof of his car to take away to the tip. It was a bushy tree and the branches were hanging over the sides in an extravagant manner. "Ah, I see you're camouflaging your car," I remarked drily.
He looked at me for a moment. "No," he said emphatically. "I had a tree come down in the storm the other night and now I'm taking it away for disposal."
After that, I couldn't stop myself from making little jokes with him. The crunch, so to speak, came when I was telling him one day about some disastrous airline trip I'd had, which had left me stranded overnight in Denver.
"Who did you fly with?" he asked. "I don't know," I replied. "They were all strangers."
He looked at me with an expression that betrayed a kind of panic. "No, I meant which airline did you fly with."
It was just after this that my wife ordered me to cease making jokes with him because apparently our chats were leaving him with migraine. The easy conclusion to draw from this, and one to which even the most astute outside observers are all too often tempted, is that Americans are constitutionally incapable of getting a joke.
I have just been reading In the Land of Oz by your own Howard Jacobson, a man of intelligence and discernment, who notes in passing that "Americans don't have a sense of humour". It would be but an afternoon's work to find 30 or 40 comments in a similar vein in modern works.
I can understand the sentiment, but it is actually quite wrong. As even a moment's reflection should remind us, many of the very funniest people who have ever lived - the Marx Brothers, WC Fields, SJ Perelman, Robert Benchley, Woody Allen, Dorothy Parker, Mark Twain - were or are Americans. Moreover, and just as obviously, they could not have achieved their fame if they had not found a large and appreciative following in their own land. So it's not as if we can't generate or relish a droll jape over here. But it is certainly true that wit is not as venerated a quality here as it is in Britain. John Cleese once said: "An Englishman would rather be told he was a bad lover than that he had no sense of humour." (Which is probably just as well, all things considered.) I don't think there are many Americans who would subscribe to that view.
Humour here is like good driving skills or having a nose for wine or being able to pronounce feuilleton correctly - commendable, worthy of admiration, but not actually vital.
It isn't that there are no people with an active sense of humour in America, just that there are far fewer. When you encounter one it is a little as I imagine it must be when two Freemasons recognise each other across a crowded room.
The last time I experienced this was a few weeks ago when I arrived at our local airport and approached a cab in need of a ride home. "Are you free?" I innocently asked the driver. He looked at me with an expression I recognised at once - the look of someone who knows a good straight line when it's handed to him. "No," he said with mock sincerity, "I charge just like everyone else."
I could almost have hugged him, but that, of course, would have been taking the joke too far.
Notes from a Big Country, Doubleday, pounds 16.99