I have a racist brother, help?

I'm just a teenager with a out of control brother and I need advice. You see when he was in middle school he never had friends and was beat up by a bunch of Mexicans, also constantly being put down by them. His hatred for this race has been going on for years. He's 19 and is old enough to be kicked out. Today, he really hurt my moms feelings by being a total ***hole to her. Both of them were at Trader Joe's today and my mom tried a sample taco, and wanted another one. He REFUSED to get her one. She's 52 years old, and does everything for him. He says that she put him in this situation on purpose, he constantly thinks everyone's out to get him. I need to tell him something that will stick and will hopefully get that stubborn brick out of his ***.