In order to demonstrate the potential for biases to develop, arrange your class into two distinct groups. Based groups upon a difference in attire, hair color or other non-offensive criteria. Have the two groups respectively engage in describing what characterizes the other group by forming a list of those characterizations. At the close of the activity, have each group read its list about the other. Observe how the comments begin to become disparaging, mocking or otherwise biased toward their own group position.
Form an activity where students question their compulsion to follow the demands of an authority figure. Without informing the class as to the intent, create a number of silly commands for them to follow, such as standing on their chairs, removing their footwear or patting their heads or bellies. Make it so the commands become increasingly odd as you progress. At the end of the session, have the students return to their seats and, either verbally or in written form, comment on what inspired them to actually obey the commands. Include instructions for explaining how the authority-oriented presence or understanding of the teacher's role influenced their decision to do so.
In terms of social behavior, gendered norms or appreciations of beauty often influence self-perception. An interesting activity for breaking through these perceptions involves finding an example of a fashion model photograph that has been de-constructed from its final form, such as the one found on the Girl Power website (Resources). The image first exhibits the polished photo of the model. You then get the option of removing the airbrushing or other adjustments made to the image so your students can see the original person. This activity goes far in illustrating how body image concerns are unfounded and how cultural appreciations of beauty are manipulated for effect and conformity.
One suggestion from the American Psychological Association (apa.org) is to offer the students a ballot before an exam. Indicate one of two choices for bonus points each would like to receive; one high and the other low. Make clear that if too many choose the higher amount, then the pool of points available to the entire class will be exceeded and no one will be able to receive points. Do not allow the students to discuss the matter before filling out the ballots. In the end, you see where the students' communal interests lie; with themselves or with the whole.