This was a long time ago, I'm not a teacher but was doing a co-op placement as an educational assistant when studying Sociology (we're talking like 15 years ago give or take).

Had a student in the class (with behavioral problems mind you) walk up to another teacher whom was pregnant and proceed to tell her he was going to cut the fetus out of her.

Nobody really knew how to react, and the tone in his voice/look in his eyes was up there with the most evil shit I've seen up till that point in my life.