Any volume which makes your music become my music too without my consent is at asshole level.

I guess no one with loud music considers themself an asshole, so this should be actually giving the information on exactly what you mention.

I spent several years in South America, and down there (it varies by country, but by and large) it's totally normal for people to play music on loudspeaker on public transport, walking down the street, in the park, etc, nobody bats an eyelid. The same behaviour in most western countries is met with disdainful looks, and often with someone else blatantly telling the "offender" to put on headphones. So, yeah, it does depend on the culture.