Fair enough, bad example.

You're still missing it. Whether something is "appropriate" or not in a given setting is a matter of opinion. It doesn't automatically mean if someone thinks someone else's behaviour is inappropriate that they will do something about it.

To use your analogy- I don't think it's "appropriate" for people to do 90 on the interstate around here like many people often do. But like you say- do I pull out in front of someone I see flying up the left lane? No, of course not.

Or, back to the eating thing, I personally wouldn't eat anything like durian or another strong smelling thing in public if it's likely to bother other people. I'm considerate, so I don't think it's "appropriate". But again, of course I wouldn't bother somebody enjoying some smelly snack.