Your karma rank is determined by the gauge next to your charge meter. Negative karma is sorted into three separate ranks:
Thug > Outlaw > Infamous
Doing anything that’s considered evil, such as completing the red side missions, doing stunts listed in red (bio leeching, killing civilians), etc., will move your karma to the negative side. As soon as you’ve reach full negative karma, the trophy will automatically unlock.
- - Side Missions that results in earning Bad Karma
Reaching full Infamous rank will NOT lock you in this rank; you'll still have to worry about your karma moving back towards the good side. You're free to save civilians once in a while, but make sure you kill a few to balance things out.