It sounds like I'm being very petty bringing these kinds of thing up, but I'll go into a bit more detail. This particular employee was extremely critical of fellow employees at his own level, and would make extremely overt attempts to ingratiate himself with senior employees and managers. We used to interview potential candidates for junior positions together. One very odd behaviour that he'd exhibit that really rubbed me the wrong way was that when we gave the applicant whiteboard tests, he would make such a concerted effort to demonstrate his superiority to the applicant by painstakingly solving and explaining the problem in gory, patronising detail before their eyes. That was how I saw it anyway, I felt that he would relish in any minor victory over other employees. I guess they call this an 'inferiority complex'. In retrospect, I feel that I should have known that someone displaying traits like these wouldn't miss the opportunity to drag me down to build himself up.