There are always people out to get more than their fair share of anything, and they are known in the dating world as users. They do not look for a real relationship with another person, and their goal is to see how far they can push another person into doing things for them. They might need someone to help their career along, or they might just want a housemate who will cook and clean for them. It can leave other people angry and frustrated, and revenge by playing a user might become a goal.
When a person is angry enough at what has been done to them, they will go quite far in trying to set things right. A former partner might find someone with the ability to be a user, and they might be able to convince them that revenge is a worthy goal. Playing another person is a cruel thing to do, but turning the tables on a person like this could help end their lack of caring for others.