Edited by Emily380 - 10/2/13 at 6:26am
I don't want to sound harsh, but your spouse needs counseling. He needs to understand sooner rather than later that his reaction to your daughter is inappropriate and potentially dangerous. 6 month olds are nothing compared to toddlers and if he can't keep his anger in check for the duration of a diaper change, he's going to have serious trouble during tantrums and other childhood challenges.
It's not abnormal to struggle with the transition to a new baby. Maybe start by asking him why he gets so upset? What is it about her squirming that makes him react that way? If he shuts down, he may need a third party to get him to realize that his reactions are not normal. But seriously, calling a 6 month old a brat is really out of line.
Does he lose his temper with you? Is he verbally abusive? I would personally think about how he reacts to other kinds of stressors and if you think this behavior could escalate, get him into couples or individual therapy ASAP. Good luck.
Do not allow him to change her diaper or even be around her until he cleans up his act. You need to be the mama bear and protect your sweet little baby from this very strange behavior. It is harmful, scary and simply not ok. Ultimatums work. "You may not be around our baby until this stops." It seems harsh, but it is not.
I agree with all of the above posts, but especially the point in this one. It may be especially tricky to get him to see how his behavior is innappropriate if he was raised that way. This is totally inappropriate though. If counseling is too expensive or he just won't go, at least invest in a couple of books describing what's normal and how to deal with it. My book is sa textbook I used in school, so maybe others have more parent oriented suggestions?
Until then, he shouldn't be left alone with the baby. Your mama bear instincts are right.