Dealing with any conflict at work can be difficult. It's especially hard when coping with a co-worker you consider abusive. The first step to take in determining how to approach this subject with your boss is making sure the behavior is indeed abusive and not an overreaction. Chronic behavior is one indicator that the co-worker's behavior may be considered abusive. Beyond that, if trying to work the issue out directly with the co-worker isn't working, or not an option because the situation is volatile, there are a few steps to take when bringing up the subject to your boss.
Gather Your Evidence
Before approaching your boss about an abusive co-worker, make note of the incidents in question. Don't give your boss vague generalities. List specific occasions when your co-worker came across as out of line. For example, instead of saying that your co-worker raises his voice to you all the time, state that your co-worker has spoken harshly to you on several occasions about an error found in a report that you produce together. Note the time, place, date and circumstances of each event to ensure you have an accurate record.
Ask For Privacy
When approaching the topic of an abusive co-worker, ask for several minutes of your supervisor's time alone. Accusing a fellow employee of being abusive is not something you want to talk about publicly over the water cooler. Make sure that no random people in your office are privy to your conversation. You could make matters worse for yourself if you are seen as a tattletale, or the subject of your conversation leaks out to the wrong person.
Keep It Strictly Business
When you do list specific examples of an abusive co-worker's behavior, keep it about business. Focus on how your co-worker's behavior affects work. Provide examples of how assignments are not efficiently completed because of his behavior, or how his behavior distracts you from your work. For example, you might say that you missed your last deadline because you felt intimidated by your co-worker, which curtailed your ability to produce calculations as quickly as you otherwise would have.
Have Back Up
You present a stronger case to your boss about an abusive co-worker if you are not the only one affected. Whether you present the topic to your boss alone or with other employees from your department, have examples ready where other people in the company are also affected by the abusive behavior. Collaborate with co-workers to come up with specific cases of abuse to present to your boss. If you meet with your boss alone, say that you are representing other employees who have also been negatively affected by the abusive co-worker.