> They are often signaling that if you want to stop them, you'll have to use violence

I'm well aware of the types you're talking about, but in my experience this has largely changed. It used to be that these sorts were the most common offenders. But now it's just, well, everyone and anyone. For instance I don't think the little, old lady in front of me on the bus the other day was challenging people to violence.

I think we're talking about two different groups of people. The ones I mean don't look dangerous, just self-absorbed. The ones you mean I don't have much experience of, they're not common around here. And they're certainly not common on airplanes.

> I saw someone get attacked with a knife, another commenter here had a gun pulled on him

I though the discussion here was about people not using their headphones on airplanes.