There is some unwritten law somewhere that brother's and sisters must fight. I know my brother and I did when we were young and my own children do as well. I've tried very hard to raise them to understand that a sibling relationship is extremely unique and special. No one else on the planet is related to you as your siblings and no one else understands your history quite as well as someone that grew up beside you.

Once in a blue moon all hell must break loose. I explain to them over and over that they wouldn't say the things they say to one another that they say to other people. That being said at 19 he's quite old enough to control his temper and behave. Try talking to him when he's calm, let him know how this behavior makes you feel.