Not acceptable.

As mentioned, perhaps the person is unaware that their headphone jack is not in. If they're just blasting noise from an iPad perhaps the person needs to be asked if they have headphones. And if the music is loud and offensive and they clearly don't care about the noise, why not deal with it with humor and say, "Would you mind putting on some Barry Manilow. Your speakers are louder than you might know". Especially on a train or long flight where they're in your immediate area.

Chuck

This thread makes me laugh. One trip to China and you will know the definition of noisy electronics....

Hey, I even get annoyed when someone IS using their headphones but has the volume cranked up so loud others can hear it too.

Small child watching videos on a generally-noisy subway/metro train: probably wouldn't bother me.

Anyone being noisy on a plane or intercity train: definitely annoying. They should have headphones. Parents should bring them for little kids.

never EVER appropriate... if this happens notify FA immediately and they will put an end to it. I cannot believe there are parents that actually encourage this behavior let alone participate in it.

You mean, like this?

Old School at its best.