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I have a coworker who neglects to perform her work properly and often acts unprofessionally (has been reprimanded for both in the past). She's also developed a habit of napping on the job, which I'm pretty sure our manager is unaware of. On top of this she is argumentative and creates an uncomfortable environment; she seems to be acting hostile to me in particular. I can't tell if the manager doesn't address this because she feels it isn't a problem or not doing anything because she doesn't know. So, where's the line between keeping your head down or saying something, especially when you feel uncomfortable around this person?