Walk the interviewer through the situation: Explain why you had difficulty with this coworker, your plan of action to resolve the issue, and the outcome. This situation could a personal matter or be regarding a specific project/task. It is important not to make your description of the situation overly negative - keep it neutral because the interviewer is looking at how you function in the workplace and how you could potentially fit into their company. You want to show that you are a team player and that you can work through difficult situations.