There is not a particular scene in Crash that I think demonstrates the issues of values and defusion, I think as a therapist you could use the film as a whole to talk about values and defusion (evaluation, that is).
The movie is about racism in Los Angeles, how ordinary people do nasty things to each other on the basis of prejudice and how people make choices in the service of their values and in the service of fear.
To start with evaluation: You could ask a client who are the bad guys and who are the good guys. The nice thing about the movie is that all the characters are doing things that hurt other people and that help other people. So there is no good or bad. And you could talk about how prejudice is something we all do, because of relational framing. And that you can ACT in a different way.
The aspect of values and commited action is closely related. You can talk with a client about the characters: When do they move in the direction of their values and when are they moving in a opposite direction. And relate this to values that clients have for themselves.
Jacqueline