What is the origin of the idiom "play the bad guy" and when to use it?

The origin of the idiom "play the bad guy" can be traced back to the concept of tough love and the idea that sometimes, in order to help someone grow or improve, it is necessary to adopt a role that challenges or pushes them beyond their comfort zone. The idiom draws on the idea that by assuming the role of the "bad guy," one takes on the responsibility of providing honest and sometimes harsh feedback, setting high standards, and refusing to go easy on the individual. It can be used in personal relationships, such as between friends, siblings, or mentors, where one individual assumes the role of providing honest feedback, tough love, or pushing the other beyond their comfort zone.