It sounds odd, but sometimes when someone (like the spaced out "gangster") gives a lot of attention (positive or negative) to a particular person, it's because they actually like them, and want to be noticed. Kind of like the old adage, "Bad publicity is better than no publicity", or dipping the girl's hair in the inkwell.
On the other hand, a bully is usually trying to take advantage of someone they perceive as more vulnerable. They have no set objective in mind, except to see how the "victim" reacts. If allowed to continue the negative behavior, it will become habit - repeated throughout adulthood.
So, is the gangster trying to win your attention? Or does he make a habit of bullying behavior with other folks at your school?
Going to the authorities (in this case, a teacher) doesn't always work. The guy gets in trouble, and ends up being mad at whoever reported him.
Is it possible to just talk to the guy when no one else is around? Not defensively, but with confidence and objectivity, ask him why he's being a dipshit (or words to that effect) and letting him know that you're not willing to continue being the fallguy to his antics.