Why do women try to hide their ass when they are in my presence. They always try to pull their shirt or sweater over their ass?

I think you are making a lot out of nothing. As little girls we are taught to keep checking on our skirts, shirts, and sweaters. Some have a tendency to ride up and this make them uncomfortable to wear. We also want a certain look and that sometimes requires us to pull the shirt or sweater down. They aren't thinking of YOUwhen they do this, they are just making sure all is in order. They don't care of you see their bottom or not. That is your problem.