Should I report this kid?

On my school bus there is a group of kids who are loud and generally jokers. They always use profanity, make fun of people, and are all around annoying to be around. There's one boy in particular who's the ringleader. He's the worst of the lot, about three or four boys in all. Normally it's easy to ignore them, but today the leader was talking about specific teachers that he hates and would want to kill. He also named kids on the bus that he would kill and the order he would kill them in. I don't really think I should take this guy seriously, because one of his "victims" was a member of his group (he said, "Next I'll kill you, because you would stop me from killing anyone else."), and because he was kind of laughing when he said it. He's a freshman and I'm a sophomore, and we've never spoken before, but I listen to this kid every single day and it's starting to become a little unbearable. He even said he would gouge out a girl's eyes because she stared and he'd kill one quiet boy because he never talked! I don't really think he would do anything, but it was very disturbing and kind of scary to hear him say those kind of things. Should I report him anonymously, or should I just let it go? If something were to happen at all, and I didn't report him, I would never forgive myself. I don't want to seem like a goody two-shoes or anything, but with Columbine and VA Tech and so many other tragedies like that, I really don't want to risk it.