Unpredictable and Unstable are the words generally used to describe a person whose behavior or conduct deviates from the usual or proper course.

Another word Capricious can be put in the same category. The word Capricious is used to describe a person who is unpredictable and shows sudden change of mind.

Your boss is such a capricious person that I wonder how he would react to my proposal.

I can’t work with you. You are so capricious and weird.