I'm trying not to get triggered by this. I had a rough break-up with a yandere gf in college. She threatened my friends. Also broke my bicycle when she found it parked overnight not at my dorm room, and filled a dorm staircase with the shredded remains of a backrest pillow of mine. As a rather advance student of Taekwondo, she didn't need a knife to be scary.
I was doing okay until the guy passively accepted sex just to get through without more drama. That cut a bit close to home. She would wear me down with wanting to get back together, and then climb into my bed to try and 'seal the deal'.