I remember from the pre-Walkman days when people would turn their radios up loud, and sing along totally out of key and in short snatches. No harm done because others couldn’t hear.
But then along came the Walkman. Many, virtually all, users would forget that people around them couldn’t hear the music that they, the user could hear. So from habit they would go ahead and do as if the radio was on and “sing” to their hearts content. Until some day when they saw someone else doing the same. Embarassing, wasn’t it? 
You’re sitting on the bus, grooving on Inna Godda Da Vida, and notice everyone’s looking at you funny.
You rarely hear anyone doing it now. Air guitar? Yes. Vocals? No.
Peace,
mangeorge
Witness Eddie Murphy, singing “Roxanne” in “48 Hours!”
Then there’s what I call “headphone syndrome.” You’re wearing headphones, got your music at whatever volume, and someone starts talking to you. You start talking waaaay louder than necessary b/c you’re talking over the music in your ears, but forget that the other person has no aural interference and doesn’t need you to raise your voice.
This also happens when I’m drunk. 
Being only 18, I don’t remember the “pre-walkman days”, as as you’ve said no one sings out loud anymore. But I can imagine it would be very funny!
In the record store where I used to work, we had listening stations where you could hear whatever new CDs we were hoping to sell. One day a guy went to the back, put on the headphones and proceeded to sing to his heart’s content, eyes closed and grooving as much as three feet of cord would allow. Stunning.
Not to hijack but , the same thing is weird about cell phones. Especially the hands free ones used in public places. It’s commonplace for a person to be standing in an isle of a supermarket having a full blown animated conversation that would be better suited for home. I’m still descreet about using mine.
…by the way… I have a theory that these are the same people who leave their carts in the center of the isle and the same people who sing with headphones on.
I hate the people who sit on a bus full of people and must have their Walkmans turned up to absolute full volume so EVERYONE can heard what the’re listening to. It must absolutely kill their ears. It’s always really shit music as well, it’s never anything you’d actually want to listen to yourself.
Yes ^^^ that’s the worst. It’s always the most awful music and they have it pumped up so damn loud. How can they stand it? How can I stand it!
Oh yeah, that too. I’d forgotten. 