Why does there have to be so many lowlifes?

i don't understand why some guy would message me calling me a whore, slut and skank when i've never done anything to him. i talked to him for a little bit and me and his sister were good friends but i didnt do anything with him he was the one who said he liked me but i told him finally that he shouldn't be talking to me cuz he has a gf. then like 3 weeks later he keeps messaging me saying he hopes i get hit by a bus and calling me and leaving me nasty messages.