leave a note on his desk.. no names, no prints

say this exactly

"hello professor, lets play a game... i have a bomb strapped to my lower abdomen and its active to explode any minute in your class room, once it detonates you and everyone else in the room will be engulfed in a fiery fury... you better wise up because if i hear another word with that negative attitude... just one word... just one word... just one."

then i guarentee he'll be nicer to you and everyone else.