I'm guessing this dream is not about violence but sexuality. You were hiding the gun, as a palvic symbol, from the cop meaning you are hiding your sexuality from authority. And to hide it from your friend might be a fear of seduction.
Someone throwing dirt on you may be some sleazy or smut. The beating I cannot guess on. Everyone beating everyone might be that you sense you are not alone in your feelings. Death in dreams represents change and being shot in the forehead may be that you have changed in the way you think.
The bad kid may be a part of yourself unto yourself even if he exists in real life. The question is what qualities do you associate with him? The whole meaning may be about a personal development. Sorry if I'm completely wrong, and good luck if I'm right.