Why don't we sing in public?

I was sitting on the train, to visit my sister. The trip takes seven hours, and I had thankfully been left alone for most of it. About halfway there, a man got on the train and sat down next to me. He took his phone out, placed it on the small table in front of his seat, and put on some football scoring service. "Great", I thought. "He is a football fan and will stay occupied with this and not bother me". When the football phone was all set up, he took out a second phone, and started playing music on it. Then he started singing along. I had to control myself to not stare at him. He obviously didn't know all the lyrics, or even the right notes, so he substituted the missing parts with loud humming. This went on until he got off the train, two stops later. 

When I told this story to my sister, we both laughed at the strange man. "I guess he was a foreigner?", my sister asked. I had to admit that yes, he was African. My talking about a man singing on the train had given her an image of a foreign person. It was apparently unthinkable that a native Norwegian would sing in public.

I was at work, late on a Friday evening. It felt like only my coworker and I were left in the mall. Suddenly, we hear a loud voice from the common area of the mall. He was singing "Halo". His voice wasn't bad at all, he could follow the complicated rhythm of the song well. We couldn't see the man, only hear his voice. My coworker and I looked at each other and burst out laughing. This made our day.

It was strange and unusual for us to hear an adult man singing in public like this. The fact that he was singing a well known song by a female singer made it even stranger. I have later thought that if it had been a child, or even a young woman, the scene wouldn't have been so weird.

Why is it seen as so strange to sing in public? At which age are we supposed to stop singing? When a child sings, people usually think it is cute. Of course, children are also "allowed" to do other things that we adults can't, such as running in public, climbing trees, and generally exploring places without a purpose or excuse.

I sometimes hum while working or walking, without a thinking about it consciously. It comes naturally. It is usually just a sign that I'm feeling safe, since I usually stay quiet in the presence of other people. Sometimes, a coworker or my SO will point it out. I usually apologise! Thinking about it, I wouldn't expect somebody who has been "caught" humming to apologise. I don't mean the kind of people who hum while people talk to them to demonstrate their ignorance. I mean just humming, as in adding background music to whatever they are doing at the moment. In some cultures, it is perfectly OK and common to sing while working. It used to be a common thing for sailors, for example.

Showing happiness in public is a good thing in my eyes. There is nothing shameful about it. The next time I catch somebody singing in public, I'll maybe smile with them instead of laughing at them.