It's best called the idiot smile, and most sports fans can relate to it. It's usually accompanied by the faraway look. You can see a lot of them around India these days - in the stands at cricket matches, in restaurants and airport lounges, at office workstations.
Behind the idiot smile lies bittersweet emotion. It's prompted by recalling the highest of highs, but it also comes tinged with the realisation that life will never get better. Spanish football fans experienced it at Soccer City last July, and the Fenway-Park faithful felt it come on when the curse of the Bambino was finally overcome. Now it's the turn of the Indian cricket fan.
The Indian Premier League's opening game, in Chennai, didn't attract a full house. A day later, in Kochi, the massive Nehru Stadium was less than half-full for the Tuskers' first game. The state assembly elections, to be held this Wednesday, might have been a factor, but the vast swathes of empty seats would certainly be of concern to owners who hadn't been especially keen to play in Kerala in the first place.
What did we expect, though? After India won the World Cup, there was a school of thought that suggested interest in the IPL could only increase as a result. Such people clearly haven't watched much sport. Or if they have, they don't understand how the fan thinks.
When your team wins the biggest honour in the game, whether that's a World Cup, a World Series pennant or a Champions League title, you experience end-of-life sensations. It doesn't always need to be a trophy either. Just ask those who were at Headingley in 1981, the Eden Gardens in 2001 or Edgbaston in 2005.
I remember staring at the empty concrete stands in Kolkata in 2001, long after players and fans had left. It was the first Test match I had covered. It may as well have been the last. How do you top that? You don't, not even if you've seen 60-odd games since.
For an entire generation of Indian fans, April 2 was such a day. Many English and Australian fans get most nostalgic about Ashes campaigns. And while there are lots of Indians who prefer the longer version of the game, the country's cricket is inextricably linked with the 50-over version. It always goes back to 1983. Just as every goal Manchester United score is a tribute to the Busby Babes, every Indian run and wicket owes something to the spirit of '83.
There comes a time, though, when the weight of history and nostalgia can crush you. Nearly three decades after that Lord's afternoon, India were getting to that stage. A new set of fans, for whom Kapil's Devils were no more than Youtube footage, needed a new focal point, something of their own to hold on to.
It wouldn't have mattered to most if they had beaten Netherlands or Zimbabwe in the final. A win is a win. But the fact that it came after back-to-back victories against Australia, Pakistan and Sri Lanka - three teams with genuine big-tournament pedigree - made it all the more satisfying. MS Dhoni and his team breathed life into the cliche that you have to beat the best to be the best.
The casual celebrity-spotting crowd will still turn up for IPL games. But for the serious fan, recovery could take a while. And any comparisons with Ahmedabad, Mohali and Mumbai will invariably be unfavourable.
The players, too, haven't been immune from the morning-after feeling - both those who were part of history as it was made and those who missed out. Gautam Gambhir will have banked about $171,000 for the one run he made in Kolkata's opening-night defeat. But who could put a price on the 97 he made in a World Cup final?
RP Singh has won an IPL (with Deccan Chargers) and the purple cap given to its leading wicket-taker. On Saturday night, playing for a new team, he looked very much like a man conscious of the fact that the most important bus had been missed. For someone who was part of the national team when the push to glory began under Dhoni and Gary Kirsten, IPL riches are poor consolation.
The discerning fan will also have noted that the expansion to 10 teams has made the gulf between the great and the average all the more apparent. It means 70 Indians are guaranteed starting places. Not even half that number have what it takes to compete on equal terms with international cricket's finest.
Had Mahela Jayawardene been captaining Sri Lanka instead of the Tuskers, he'd have thrown the ball to Lasith Malinga for the 18th over on Sunday. Instead, he looked around at a threadbare attack and settled on Raiphi Vincent Gomez. Three mighty AB de Villiers sixes later, the match was as good as over.
Even if the overseas quota is increased to five players - and for that to work, Pakistani players will have to be welcomed back - most teams will still have a popgun bowler or out-of-his-league batsman who can be picked on. However great the hype - and the commentators seem to be outdoing themselves even in Lalit Modi's absence - the lack of depth can't be wished away.
Club football is a different beast. With no salary cap in place, the likes of Real Madrid or Chelsea can hoover up available talent, even if that means stars rotting on the bench. The IPL's insistence on a homegrown quota makes it relevant to a local audience and keeps the playing field even, but it also means that you won't ever see a team that can match the excellence of Ponting's Australia (2003-07) or the batting depth of Dhoni's India.
One of the most eloquent takes on the nature of fandom, its ecstasy and agony, is Colin Schindler's Manchester United Ruined My Life. Two decades from now, you can expect a similar treatise from a middle-aged Indian. Only, this one will be called How Dhoni Ruined Everything. One fluid swing of the bat, the ball soaring into Mumbai's night and a foothold on cricket's highest peak. You can only go downhill from there.