Yeah, I had someone who was extremely paranoid and definitely in need of help who started sending me private messages accusing a mutual friend of doing all sort of horrible things to them. (I knew the person they were accusing in real life but they were someone I knew only online.) They wouldn't listen about getting some help so I blocked them. Then they created fake accounts to send me messages and then blocked me before I could respond. Facebook definitely brings some problematic behaviors to light, for sure.