I do get that. You may just have to find ways to shield yourself from your brother when you want to see the cousins and have family get togethers. I imagine that they last a few days, and if that's the case you don't have to be there 100% of the time. when he acts out, leave - at least leave the area, walk away. he's a man child like you say and he lives for the angry attention he gets and your response you give when he does so. This is his reward he loves. So refuse that reward and do the opposite, do not react, ignore, walk away for the moment and continue with your visiting with other people. In time I think you'll find he will give up if you're consistent.