Something that has changed from good to bad, likable to unlikeable, usually referring to a person. Often, there is the possibility that said person is now a jackass because he has been replaced by The Thing.
MacCready and Palmer are friends. Palmer tries to kill MacCready and all of their other friends in their cool snow-fort.
Palmer is said to be infected.
Lynch and Larry hang out a lot. Larry stops calling Lynch for no reason. Larry is said to be infected.