Aggressive and mean employees are hard. They often deny behavior, say others are lying, or try and strong arm you out of setting an expectation. Yeah, managers can be bullied too. Soome managers are either afraid of an employee or just dread trying to talk to them. It is important to protect the work environment for all staff, so, mean employees need to be dealt with. However, check your bias and the bias of others. And consider if any medical leave like fmla (maybe the person is highly stressed