My apologies to Samuel Johnson, but London is no longer a reliable guide to whether a man is tired of life. The true measure in modern times is Paris. When the French capital's charms no longer touch you, you know you might as well give up.
Yes, there are moments when its travel-book clichés pall a little: when you gaze at the Eiffel Tower and see only a giant syringe shooting the city up in broad daylight to feed an embarrassing tourism habit. But in Paris, even the clichés are renewable. Pass Gustave Eiffel's creation during the light-show - a nightly event since the Millennium celebrations - and you may find yourself gazing again in slack-jawed wonder, like you did the first time.
So synonymous with Paris has the tower become, the wonder is that it was never intended to be permanent. It was built for the Exposition of 1889, with a concession for 20 years, after which the 7,000 tonnes of metal was to be dismantled. Even as a temporary exhibit, many considered it a monstrosity. And it survived the guillotine in 1909 only because its antennae had become vital to the development of radio telegraphy.
A century later, it is impossible to think of Paris without this object that allows it boast to other cities: my phallic symbol is bigger than yours. The tower is the inspiration for countless Freudian poster advertisements. Even the Paris Gaels GAA club - who gave a skills demonstration at the weekend - have an ingenious version of it on their jerseys: two hurleys leaning against each other back to back with a football underneath.
The Parisian obsession with sex in general is no doubt exaggerated. But it can be difficult to escape the subject there (assuming you want to). Even the normally sober Musée de l'Armée is currently running an exhibition on the theme "Amours, Guerres & Sexualité 1914 -1945", featuring everything from Mata Hari's well-stamped passport to erotic drawings of nurses in army hospitals.
Of course the question always arises whether it's you or Paris that has sex on the brain. Visiting the Irish Embassy for the first time, I couldn't help noticing its risqué location: on the corner of Rue Rude and Avenue Foch. That seems like a challenging address, even for diplomats. Then again, as I was informed by the lady in reception: (1) Monsieur Rude was just a sculptor who worked on the nearby Arc de Triomphe; and (2) the "ch" in "Foch" is soft.
THE ONE THING Parisians do probably think about more than sex is food. And for all its urban decadence, one of the charms of Paris is that it is also the capital of an incorrigibly rural country. You think Ireland is still agricultural until you go to France and discover that, for example, they have something called la folie des champignons - mushroom madness - which is sweeping the country even as we speak.
The condition is at its mildest in Paris, where restaurants are tempting customers with such dishes as boeuf aux cèpes. In another symptom, cèpes - the filet mignon of mushrooms - currently fetch €45 a kilo in the city's food markets. But the real folie des champignons happens nearer the source, in the forests where the prized fungus grows.
France has strict laws about who can pick mushrooms where, and how. Authorised pickers are required to use wicker baskets, to allow spores to fall out and propagate. But with unauthorised picking rife, security guards are sometimes hired to protect privately owned forests, and violence occasionally results. The International Herald Tribune wrote recently of "noses broken, windscreens smashed, and tyres slashed", and of large fines levied on "professional traffickers".
It's not all about cèpes, either. Charles de Gaulle once complained about the challenge of uniting a country that had "265 kinds of cheese". He could have said something similar about mushrooms. One consequence of the nation's passion for them is that every French pharmacy has to have a mycology expert on the staff who can identify samples brought in for inspection. The idea is to stop people poisoning themselves. But occasionally they do anyway.
Mushroom eaters are hospitalised every year and, not infrequently, there are fatalities - usually after someone mistakes the "death cap" for something more benign, such as the agaric des bois. And yet the dangers do not deter enthusiasts, the more committed of whom go foraging before dawn, sometimes wearing miners' lamps on their heads.
Mushroom madness can affect you in more ways than that. The IHT writer reported experiencing "geometric hallucinations" recently after eating wild French mushrooms (which, he added, were "delicious" when cooked with butter and garlic), despite having them vetted first by two different pharmacists.
He also cited studies that have suggested a link between the contrasting motifs in primitive art and the different mushrooms available from region to region. And he quoted the writer Terrence McNally (no relation) speculating that fungal hallucinations were a rare example of inter-species communication.
That, in effect, "the mushrooms are telling us how the plant kingdom thinks". It's a spooky idea. Despite which, I had mushrooms with everything in Paris last weekend, and very nice they were too. They caused no hallucinations that I remember; although, now that I think of it, there was an hour or two after lunch on Saturday when I could see the Irish rugby team beating Argentina by 35 points.