On Coase and Income

I hope my international economic policy students can answer this:

Economist Ronald Coase argued that in cases where one person involuntarily harms another through their actions, (also known as a negative externality, such as a factory emitting smog on a community), that the group who should change their action is the one who is the least cost avoider (for example is it less costly for the factory to move than the community). How does income inequality create a negative externality? In the case of income inequality, who is the least cost avoider? Justify your answer.