Is this confrontational person a bully? Could they be feeling that their job would be threatened, if you do well? How does this person treat others in the office? If there seems to be a co-worker that appears to be not at all threatened by this problem person, maybe you could confide in that co-worker that seems to be unfazed by this bully. They might be able to give you some insight into what the real problem is with this confrontational person.