Long before Mayor Michael Bloomberg banned smoking in New York's bars, your typical Big Apple hostess had banished the stinking habit from her apartment. That mass expulsion had a strange result because gatherings to celebrate things like last Sunday's Super Bowl now tend to schizophrenia, with two parties going on simultaneously - one in the living room, the other down the hall in the nearest stairwell.

Smoking indoors is illegal - everything is these days under Mayor Wowser - but a sociologist could have a field day with the odd little conventions that now surround the outlaw habit.

What are the unspoken cues that alert some barmen to the departure of the last potential tattle-tale and prompt the unbidden appearance of illegal ashtrays?

Like most conceits and deceits, those behavioural ticks tell you quite a bit about the society that indulges them.

Take the fickleness of shock and horror, for example. It erupted in spades at half-time of the big game, when the biggest "wardrobe malfunction" since the closet door sprang open on Liberace brought the infamous exposure of Janet Jackson's right breast.

As late-night comic Jay Leno observed, when Justin Timberlake remodelled his co-star's bustier, it was the first time a Jackson had ever been the victim of a molester.

At the East Side game party I attended, the squeal of surprise was louder than a touchdown and brought the smokers piling back to find out what was what.

"Why the yelling?" asked one.

"Somebody shoot Bush?" cracked another in a voice that spoke of wishful thinking. This is an election year and partisan sentiments are rising, so talk of knocking off your President - a weakness America has indulged more than most - isn't in good taste. All the same, since this was New York, where Democrats win just about every election all the time, only a couple of those present took extreme offence.

One was a petite woman with a pixie bob, whose ire turned out to be other than politically inspired. She fixed the joker with an especially sharp eye and said, almost snarled: "Smoking again. You're pathetic." Turns out she was the offender's recently discarded girlfriend, and that an RSVP snafu, for which the hostess apologised in whispers all night, had reunited two people each of whose surprise at finding themselves in the same room was exceeded only by the other's contempt.

The former beau mumbled something about really, seriously being off the butts. It was just that he indulged socially, not that those moments mattered, of course, because he was genuinely, absolutely an ex-smoker - except, apparently, when he wasn't. It's a common deceit in America, where a decrease in cigarette sales comes nowhere near matching the increase in those who claim to have reformed.

She sniffed and turned away to rejoin the room's babble about Janet's boob. From people loved or even merely liked, lies and self-serving fictions can be indulged. But when the heart has turned, no more.

It's the same problem George Bush is facing now that those dossiers about Iraq's illegal weaponry don't seem half so persuasive as when Colin Powell lectured a hostile United Nations. September 11 was fresher, and the instinct to rally around the leader less restrained. There seemed no need then to render the wealth and breadth of arguments for taking out a tyrant in anything but verbal shorthand: WMD.

As Paul Wolfowitz put it, there were other reasons Saddam had to go, but WMDs would do the trick.

UN reports of unaccounted poisons and footage of gassed villages didn't hurt either. Since the Iraqis weren't saying where or how those toxins were destroyed and the UN couldn't find them, it stood to reason that Baghdad must still have stockpiles of nasty stuff for killing Kurds and others.

Focusing on the gas and germs also ducked the embarrassment of the most compelling reason to put the tanks in gear. No need to mention how Bush the Elder encouraged Iraqis to revolt after the first Gulf War and then betrayed those who listened to Saddam's vengeance. Best to overlook that little exercise in treachery and the moral obligation to redress it.

And anyway, time was of the essence. All those troops in desert staging camps couldn't cool their heels forever. So let's kick the ball out of the trenches, went the White House line, get the offence on the field, and roll like the Super Bowl's champion Patriots toward a Baghdad touchdown.

With the exception of a minority's chants that it was all about oil, few Americans needed a fuller explanation. Saddam was a bastard and had to go, that was the bottom line. Even Senator John Kerry, now riding the wave of post-war disenchantment that will likely carry him to his party's nomination, voted for invasion. The instant reaction carried the day - as it did with the Super Bowl outrage.

"So if it wasn't planned, why was Janet wearing that star on her nipple?" demanded the hostess. All present agreed that they, too, were shocked. One guest even noted that her twin 12-year-old boys were in the room, and how dare CBS expose their innocent eyes to that sort of sleazy stuff?

And then a curious thing happened. The hostess observed that it was time for Sex and the City and the women migrated as a body to the bedroom TV, leaving their guys to catch the game's second half and cheer and punch the air alone.

One of the twins followed and if any of the women thought to toss him out, none did. Apparently a serial heavy on nudity and wholesale humping was acceptable fare for kids on one TV set, but a rogue bosom on another went beyond the pale.

Go figure. Like America's ongoing decision to review what once was clear and obvious about Iraq - that Saddam was a mass murderer and a potential threat - perception is about the mindset of the moment. From cigarette smoke to TV sex and 300,000 bodies in Saddam's mass graves, what we know isn't half so important as the how, when and why of choosing to ignore it.