At the most basic level, an underlying rule in all English conversation is the proscription of 'earnestness'. Although we may not have a monopoly on humour, or even on irony, the English are probably more acutely sensitive than any other nation to the distinction between 'serious' and 'solemn', between 'sincerity' and 'earnestness'.
This distinction is crucial to any kind of understanding of Englishness. I cannot emphasize this strongly enough: if you are not able to grasp these subtle but vital differences, you will never understand the English - and even if you speak the language fluently, you will never feel or appear entirely at home in conversation with the English. Your English may be impeccable, but your behavioural 'grammar' will be full of glaring errors.
Once you have become sufficiently sensitized to these distinctions, the Importance of Not Being Earnest rule is really quite simple. Seriousness is acceptable, solemnity is prohibited. Sincerity is allowed, earnestness is strictly forbidden. Pomposity and self-importance are outlawed. Serious matters can be spoken of seriously, but one must never take oneself too seriously. The ability to laugh at ourselves, although it may be rooted in a form of arrogance, is one of the more endearing characteristics of the English. (At least, I hope I am right about this: if I have overestimated our ability to laugh at ourselves, this book will be rather unpopular.)
To take a deliberately extreme example, the kind of hand-on-heart, gushing earnestness and pompous, Bible-thumping solemnity favoured by almost all American politicians would never win a single vote in this country - we watch these speeches on our news programmes with a kind of smugly detached amusement, wondering how the cheering crowds can possibly be so credulous as to fall for this sort of nonsense. When we are not feeling smugly amused, we are cringing with vicarious embarrassment: how can these politicians bring themselves to utter such shamefully earnest platitudes, in such ludicrously solemn tones? We expect politicians to speak largely in platitudes, of course - ours are no different in this respect - it is the earnestness that makes us wince. The same goes for the gushy, tearful acceptance speeches of American actors at the Oscars and other awards ceremonies, to which English television viewers across the country all respond with the same finger-down-throat 'I'm going to be sick' gesture. You will rarely see English Oscar-winners indulging in these heart-on-sleeve displays - their speeches tend to be either short and dignified or self-deprecatingly humorous, and even so they nearly always manage to look uncomfortable and embarrassed. Any English thespian who dares to break these unwritten rules is ridiculed and dismissed as a 'luvvie'.
And Americans, although among the easiest to scoff at, are by no means the only targets of our cynical censure. The sentimental patriotism of leaders and the portentous earnestness of writers, artists, actors, musicians, pundits and other public figures of all nations are treated with equal derision and disdain by the English, who can spot the slightest hint of self-importance at twenty paces, even on a grainy television picture and in a language we don't understand.
The 'Oh, Come Off It!' Rule
The English ban on earnestness, and specifically on taking oneself too seriously, means that our own politicians and other public figures have a particularly tough time. The sharp-eyed English public is even less tolerant of any breaches of these rules on home ground, and even the smallest lapse - the tiniest sign that a speaker may be overdoing the intensity and crossing the fine line from sincerity to earnestness - will be spotted and picked up on immediately, with scornful cries of 'Oh, come off it!'
And we are just as hard on each other, in ordinary everyday conversation, as we are on those in the public eye. In fact, if a country or culture could be said to have a catchphrase, I would propose 'Oh, come off it!' as a strong candidate for England's national catchphrase. Jeremy Paxman's candidate is 'I know my rights' - well, he doesn't actually use the term catchphrase, but he refers to this one frequently, and it is the only such phrase that he includes in his personal list of defining characteristics of Englishness. I take his point, and 'I know my rights' does beautifully encapsulate a peculiarly English brand of stubborn individualism and a strong sense of justice. But I would maintain that the armchair cynicism of 'Oh, come off it!' is more truly representative of the English psyche than the belligerent activism suggested by 'I know my rights'. This may be why, as someone once said, the English have satire instead of revolutions.
There have certainly been brave individuals who have campaigned for the rights and freedoms we now enjoy, but most ordinary English people now rather take these for granted, and prefer sniping, pinpricking and grumbling from the sidelines to any sort of active involvement in defending or maintaining them. Many cannot even be bothered to vote in national elections, although the pollsters and pundits cannot seem to agree on whether our shamefully low turnout is due to cynicism or apathy - or, the most likely answer, a bit of both. Most of those who do vote, do so in much the same highly sceptical spirit, choosing the 'best of a bad lot' or the 'lesser of two evils', rather than with any shining-eyed, fervent conviction that this or that party is really going to make the world a better place. Such a suggestion would be greeted with the customary 'Oh, come off it!'
Among the young and others susceptible to linguistic fads and fashions, the current response might be the ironic 'Yeah, right' rather than 'Oh, come off it!' - but the principle is the same. Similarly, those who break the Importance of Not Being Earnest rule are described in the latest slang as being 'up themselves', rather than the more traditional 'full of themselves'. By the time you read this, these may in turn have been superseded by new expressions, but the underlying rules and values are deep-rooted, and will remain unchanged.