My little brother is turning into a coldhearted ***hole I dont want him 2 be help a criminal or a jerk! help!?

My little brother 16 is trying to be a little thug but at home he's a quiet mommy's boy. but at school and stuff he a "thug" goin around talkin bout how he has guns and would kill people easily and was in a gang. he already got arrested once for a wachin a fight he just went 2 juvie for a few hours but now that just make him feel he's even more of a thug and he brags about it and im afraid he may go back. then on his myspace page he wrote its a shame I gotta tell a B**** I love her to get some. he's talkin bout ho's and violent stuff. I recently went thru a bad sit. with an ex who was a jerk who pretended to love me 2 sleep wit me. and I dont want my brother to be like him. I tried talkin to him and about how it hurt and that i was even suicidal 4 a bit and the lil idiot was like "damn u shouldve gotten a gun at the pawn shop and shoot urself in the head" wit a straight face and i was like dats harsh and he was like so. Im growin ill feelings 4 him how 2 help him change.