The other day, Miss Nancy dell'Olio was asked by a newspaper to describe her day, in her own words.

The result, though full of character, raised quite a few eyebrows. Miss dell'Olio, it is fair to say, is in no illusion about her own personal qualities. There is a game that English people like to play, in which players guess the least likely phrase to be used by a well-known figure in conversation. Nancy dell'Olio's, possibly, might be "Oh, I wouldn't go as far as to say that."

Talking about herself, she said: "Since I was a little child in Italy, people have looked at me, and not just because I'm beautiful; it's something else that comes from inside me. I know I'm fascinating... I'm a very loved person. Women and men, they both love me, and this is because I'm the kindest person I know... I love the opera. [My new partner, Trevor Nunn] said already I'm the most intelligent person he's ever met. I'm sure the majority of people haven't sat through seven hours of Wagner as I have."

There was some amusement at this innocent self-portrait – Twitter was briefly ablaze – and some less generous comment, too. A Miles Nicholls wrote in the online comments: "I have never read about a more arrogant, self-obsessed woman. She is totally mad." Others hastened to point out, showing some preening self-regard themselves, that they had never heard of Nancy dell'Olio. One, calling herself "English Rose", wrote "We, the English, are masters of self-deprecation and this is the antithesis. She is supposedly my age except I am a very successful lawyer with a very large family and she seems to do very little."

Why it is unacceptable to say "I'm very beautiful" and acceptable to say "I am a very successful lawyer" is an interesting point. The rules of boasting, of the acceptable display of self-esteem are in flux. If you pick up the newspapers, read a random blog, watch the television, you won't have to wait long before somebody offers up part of their life for your admiration. It is, apparently, OK to boast about the size of your house, the amount of weight you have lost, an expensive holiday you've just taken. Those are described as "achievements". Intelligence, the preservation of good looks and health, good manners: these, on the other hand, don't seem to be appropriate topics for boasting.

Boasting, like flirtation, is a social activity with strict rules. In the act of boasting, the successful boaster detaches himself from his identity, and pretends to observe it from a neutral stance. It is more convincing if the object of the boast can be detached from the boaster's physical presence to some degree. One boasts not about one's face, voice, body, mind. But some degree of pride is possible about a work project, a house that has been remodelled (people are never so innocently boastful as when discussing building works on their homes), perhaps a book that one has written, and those detachable entities, one's own children. It only seems to be acceptable to boast about physical facts and properties when they are the direct product of some drastic change.

Boasting about processes – weight loss, education, the acquisition of a skill, the successful conclusion of therapy – is possible. You can't boast about being thin, or kind. But boasting about becoming thin through lots of boring exercise, or kind through the attentions of your therapist: that seems allowed.

And once something is too detached from you, and not the product of your own labour, then it becomes unacceptable once more to boast about it. Put it like this: it might be all right to boast about an actor friend getting you a pair of tickets to his opening night. But to boast about buying tickets for the second night of the run would be a waste of energy, reflecting on nothing but your wallet. You can boast about the achievements of your immediate family and your close friends, I believe, often hiding pride in your personal association beneath a genuine wish to congratulate. But beyond a certain intimacy, it becomes unseemly to mention that your child's headmaster was invited to a Buckingham Palace garden party, say.

There are no easy ways through this minefield, and the simplest option is to opt out entirely. There are people who, admirably, never mention that they have just published a biography of Metternich, or been promoted to senior librarian, or given birth to twins, and greet any spontaneous congratulations with a smile and a "thank you". But, since the 1970s, we have been told that the key to personal happiness and fulfilment is a sustained and realistic level of self-esteem, one which accords with our achievements. The rest of the world has an annoying habit of not noticing our biographies of Metternich, being under the impression that we were always senior librarians, not much caring about Charles and Charlotte's existence. If we sat there waiting for the spontaneous admiration of others, we would be there forever, fuming slightly. And so we boast.