Crowds make Games. They give them a humour and heart. They give them friendship as the English did in 2012. They give them the tuneless "Aussie, Aussie, Aussie, oi, oi, oi" as happened in 2000. They give them, as the Brazilians did, the unrequired boo.
The Rio crowds adored Bolt, loved Phelps and rightly tested the rivets holding down stadium roofs when the Brazilians played. They were terrific: Fun, noisy and ready to dance.
But they also booed, jeered and whistled. Not all of them, but some. Not at all athletes, but a few. In the athletics to a pole vaulter. At the beach volleyball to my astonishment. At the swimming with rare ugliness. Even at the table tennis.
Booing and sport are old pals but it's not so common at the Olympics. It happens, but not often. Why? Because hosts are usually nice. You know, welcome world and all that.
Of course it's important to learn a little about the local culture, which includes booing in football. Even at Neymar. And as guests we don't want to really make a loud boo and cry about anything.
But, really, jeering Olympians is lame and rude. These aren't overpaid celebrities who aren't giving effort. These are fencers, for God's sake. This is heckling someone who does two jobs and still trains.
These were a lovely Games, ironically full of music. But those occasional jeering notes? They looked bad and sounded worse.