This is a very difficult challenge.  People have offered some great ideas: 1) remind students of the big picture (why they are back at school) and hold them to the expectations that you set at the beginning of the course.  I teach general education courses, so I am always trying to emphasize the practical importance of the course material in order to motivate my students.

@mskala03d :Miriam, I really like this idea of having students contribute to the list of rude behavior.  They are less likely to exhibit a behavior if they had a role in devloping the list.