I always assume people doing this are unhinged/crazy and I definitely don't want to deal with that.

Sometimes they look nice enough.

Usually what happens is myself and everyone else on the train look at each other, have a shared look of "Morons? Am I right?" and then when that person leaves, we all share a group laugh.

So I guess what I'd say is, if you do this, know that everyone is laughing at you. If you say you don't care, that's a lie, you do care, that's why you're doing what you're doing. This is not positive attention, this is negative attention. Please take a moment and reflect to be a force for positivity and not negativity.

The venn diagram of people who play music on speakers in public and people who are a thin thread away from stabbing you is a circle.

Also, I live in the US, so the medical fees for getting stabbed is not worth the risk.

I'm not trying to get stabbed in the neck. You should consider this risk too.

Why is it always the worst rap music imaginable? Like, I'm a hip hop fanatic, old school, new school, trap, g funk, boom bap, conscious, etc. But why is it the most asinine "i took a xanny now i'm fucking your girl" type shit?

Nope, not worth it. I've stopped trying to convince others to be considerate in public. They'll either ignore you or blow up and get aggressive. I'd rather just try to ignore them myself and move on with my life.

And at the end of the day, I'm also not some authority figure like their mom or dad; I'm nobody to them. As much as I may not always like it, strangers don't owe me anything, including their consideration.

I've tried this. Guy next to me was playing a video game on full blast that I can hear over my noise cancelling headphones. I asked him if he could turn the sound down.

He said "F you! This is my console. I do what I want! You're the only one complaining so shut the f up".....

Start up your Bluetooth speaker. (Buy one if you haven't got one. It doesn't have to be good, just loud.)
Ramp it up to 11.
Start the most annoying obnoxious sound you have, (that you have already downloaded).
Stand next to the person playing the shitty music and aim the speaker at then.
When they complain about your annoying noise you reply, "You started it."

i wonder what would happen if you just start acting really into it and singing along terribly with enthusiasm.

Yeah I don't need the tweaky dude stabbing me on the train because I didn't like his music, but thanks

I'm American, I'm not trying to get shot

German here. A woman was starting to play loud music on her phone while I was sitting at a bakery having a cup of coffee, trying to relax from a bad morning. I opened Spotify, checked for this song: https://www.youtube.com/watch?v=PDBDtIOxUsI Every Maaaaaamaaaa I was singing loudly along. She lasted half of the song then fled the scene, even left her coffee on the table. My ears were bleeding, but it was worth it.

Fight them with the most terrible old people song you know in your country, be aware that it might hurt you too.

You better have the gun from the meme if you're gonna make a habit of this.

Yes. We shoot people for accelerating from a stoplight too fast here.

Try that in a big town

Yeah I mean I'm not much of a fighter and I've gotten put in the hospital for something similar, so now I avoid confrontation like the plague.

I envy your bravery

In Australia these people are deros huffing glue or drinking bowlers run red wine from the bottle. No thanks, I'd rather avoid them.