My use of the term "egoboo" isn't mean to be derogatory; I just like the word. (Try saying it out loud. Egoboo! Egoboo! It's fun.)
I'd divide things on a finer scale than you do. It isn't just music; it's particular instruments more than others. Noodling around on a guitar at a party will go over a lot better than doing the same on a tuba. That's probably the most socially-acceptable "hobby instrument" I can think of; violin and piano are in there, too, as might be a flute or tin whistle in a Celtic or folk music context. You could probably list more, but it does depend on the instrument, the genre of music, and the social context, which ones can be done casually and which ones can't. (Meaning "can" and "can't" in a social-perception sense, not an absolute one.)
Re: $0.02
I'd divide things on a finer scale than you do. It isn't just music; it's particular instruments more than others. Noodling around on a guitar at a party will go over a lot better than doing the same on a tuba. That's probably the most socially-acceptable "hobby instrument" I can think of; violin and piano are in there, too, as might be a flute or tin whistle in a Celtic or folk music context. You could probably list more, but it does depend on the instrument, the genre of music, and the social context, which ones can be done casually and which ones can't. (Meaning "can" and "can't" in a social-perception sense, not an absolute one.)