Principal, guidance councilor, etc.. If the PE teacher isn't taking it seriously, that should be addressed as well. We here in the Denver area tend to be rather insulated, still, from the realities of school violence. The over-reaction to recent video projects from Boulder high school demonstrates this odd dichotomy. The fact is, any threat of violence should be taken seriously. It might be hot air, and it might not. Don't wind up in a trauma cubical at DG just because you weren't sure. Similarly, you don't want to end up in jail as partt of the "zero tolerance" policy.