I'm furious and I don't know how to approach my husband about this. UGH!! Advice?

Our son is 3.5 years old. My husband is frustrating me SO MUCH, and tonight may has brought me to my boiling point. We have a daughter who is 9 months old. My husband openly favors her, talking sweetly to her and literally turning around and barking an order or even cursing at our son. Every time he does I ask him politely (so we don't appear to fight in front of the kids) not to talk to him like that. BUT... our son has always had some weird behavior quirks like lining up all his toys and other objects and being obsessive about the yarn on his quilt, as well as some other things. He has these total meltdowns over the tiniest things, like his sandwich falling apart. We have to take him in for a behavioral evaluation because he may have something called PDD, which is similar to Autism. Today our son was having a violent, screaming fit, and was wringing his hands over and over, and I called my husband in to see. He came in, looked and yelled, "Yeah! I know my son's a f'ing retard!" hit the door and stormed out. He called my son a retard and my son was RIGHT THERE. yeah, he may be having issues accepting the fact that somethings wrong with our son bu COME ON. I'm so furious I don't even know what to do. I'm afraid if I bring it up right now I'm just going to explode and we'll get into a nasty fight. I'm so pissed. How am I going to approach this when it upsets me so much? I'm literally shaking right now and this happened 2 1/2 hours ago. I can't get over it.