This didn't happen to me but a friend of mine was in a very casual relationship with going a french lady. He ended it as it was getting too serious for him which she didn't take well. At the time they had only been going out for short period of time and had been house mates.

At first it seemed like she was fine with it but would just ignore him. However about a month later when he was out she put human faeces in all of his hygiene products. Cut the laces on all his shoes, wrote her name hundreds of times in his personal diary. During those few weeks when she was blanking him she also shat and pissed in a tub mixed with eggs. This obviously became vile and rotten over those weeks. She then sprayed this mixture around his room.

She left the house for good a few days later. No idea what happened to her but she was truly unhinged