First, you cannot save him from himself. Apparently your parents have allowed his behavior to escalate and it is just a matter of time before, like you say, he pisses off the wrong people. They will surely "teach" him a lesson, but at what price is yet to be seen.
Since your parents will not do anything to control your brother, it is up to you to just walk away from him when he gets in a violent mood. Yes, just get up when you notice the signs of his emotional state deteriorating and leave the room. Since he is irrational, nothing you say is going to calm him down because reasoning with him while he is in a fit of rage goes unheard. So, the only thing for you to do is to remove yourself from the situation.
It is such a shame that your parents have not disciplined your brother because he is in for a rude awakening once he ages a few more years and realizes that authority, real authority are not softies, like your parents. Be prepared for your parents to bail him out of all the trouble that lies ahead.
His personality is pretty engrained in him by now, so unless your parents force him to get some professional help, he will just spiral downward until he is so deep into trouble that the judicial system will take over where your parents left off.
All you can do is to be the best you can be and soon enough, when you leave home, you will be free of his dysfunctional behavior.