Nothing related to gender, but I once had a coworker at a mid-sized company angrily threaten me in his cubicle: "if we weren't in the office, I would slit your throat." I immediately went to HR about it and literally the first thing they asked me after I told them was "can anyone corroborate your story?" I couldn't since nobody overheard us, so I was screwed. It was the only time in my life that I actually feared for my life from another human being -- especially since I tried to report him. I walked to my car with a friend that night, fearing he'd be waiting for me in the parking lot.

This coworker had received complaints for other issues from others in my department as well, but the company just didn't act. He remained there until he finally was fired for incompetence.