Q. "What's the best way to approach a new employee with a bad attitude?"
Answer:
It is important to make the employee aware of your concerns. If they haven't had any specific feedback yet, make sure to include it in their 90-day review as well as document this conversation and the expectations you set.
Specify which behaviors need to change and communicate what they should be going forward. Keep the focus on the culture of your organization helping them understand the “why”. If they understand your reasons, they might be more open to instruction. Give them a chance to voice and discuss concerns, as well.
Reassure them that you recognize they are in a learning period, but you expect them to be open to constructive criticism and get along with the team.