Help? advice?

mark has been my best guy friend for as long as I can remember. people always tell me I should go out with him. this other boy I like, daniel, likes to annoy me. he will randomly come out behind me in the halls and say ';I'm going to kill you'; then gives me this creepy look. he acts serious when he says it but he is joking. I wanted mark to meet daniel and mark was like ';I don't need to meet him, I already know who he is, I saw you talking to him earlier';. is mark jealous? when daniel comes out of no where to talk to me and say that, is he trying to flirt with me or just annoy me? help!!! what should I do to get daniel to stop saying those things?Help? advice?
What he is saying isnt funny...I would tell a teacher, your parents...someome....

jabbawockeez mask