How do I get this person on facebook to leave me alone?

[Bitterbat845]

This person on facebook who's my age doesn't leave me alone. He is friendly but he's so annoying. He also wants to date my sister and he has 3 girlfriends. He also acts like an idiot saying "seig heil" and putting emo pictures. He also said one time that he wants to commit "suicide". I think he was expecting sympathy. I don't give sympathy to people who want to commit suicide. How do I tell him nicely to leave him alone? Plan B is to troll him hard.