...and if you do, don't go showing it around!
Everyone harbors thoughts about blowing people away; on more than one occasion I've talked about how I wish I had a button on the dashboard of my car that would allow quad .50-cals to rise from the hood to get rid of some idiot driving in front of me. However, that's so far divorced from reality (how would the 50's fit in there with the engine?!), and so general in nature, that no one should fear that I'd actually do it.
However, people have brought firearms to schools and started shooting. In my own district a very disturbed middle schooler was going to shoot his science teacher; she bolted out of the room and I don't blame her a bit, as no one pays us to take bullets from or in front of students.
Writing about wanting to kill your teachers, in these post-Columbine days? Not a smart idea. The student in the linked story above deserved her suspension.