Being the nanny for a 12 year old.. please help me, how do I handle the disrespect?

It sounds like an unhealthy environment for you to put yourself in. It isn't your job to care for the little whinge's future or put up with his shtick beyond reason. If the father's ignorant enough to not trust the report of a grown woman, you might want to throw in the towel and find a different family to sit.