A female coworker who was also a close friend of mine sent me an issue, asking me if it was related to an issue I had debugged. It was, and the issue was not assigned, so I took it and closed it as duplicate.
She was pissed. She wanted to know if it was a simple issue so she could assign it to herself, close it easily and get credit for it. (Not that our group really used that as a performance metric.) She actually said to me: "That was really unprofessional you ass!" I tried to gently suggest that she might be taking it too personally. If I had realized she wanted to close the issue herself, I probably would have let her. I just closed it myself because it was faster.
Later she told me that she had read in a book that women tend to become more emotionally invested in their work than men do. I told her I was glad she had read that in a book.
I'd rather deal with someone who is obviously pissed at me than someone who is secretly pissed at me any day of the week.
(The passive aggressive thing has been much, much more prevalent amongst nerds, in my experience, compounding the problem)
For me, it's been nerds and women.
On the other hand I can remember a colleague of mine not talking to one of our teammates because of a personal reason. This, i think, affects business.