How do I tell my brother his lady is a snob?

My brother is a year older than I am and we are very close. We never really fought until it came to his choice in the ladies. His first girlfriend was as dim witted as they came and now he just expressed he's going to be marrying his current nightmare. She's not that rich or anything but she acts as if she's the queen of everything. Just the other day she didn't like my baby cousin Sarah looking at her so she cut off sarahs bangs. She told me the toddler deserved it and looked down on me then told my aunt that sarah cut her hair off. And I told my aunt different but she believes that my brothers fiancee is an angel. I don't know how to approach him about it without severing a precious sibling bond. any suggestions?