What happens with my family (everyone is either mixed, Asian, or Hispanic) is that people forget that we're not lily white because most of the people around us are--and they'll make some crack and then remember. Then they spend the next month apologizing. I hate that.
Of course, there are also people who walk right up and say rude things. My husband is a deacon at church and the church also has a Latino ministry. Last Christmas, this elderly woman walked up to him as he stood with my Guatemalan daughter and me and said, "Here's my Christmas offering. It's not going to any Mexicans, is it?"