"I'm tired of playing the brat"

In this quote, Casey Affleck is expressing his aggravation with a certain role he has actually been playing. He is tired of playing the brat, which suggests that he has actually been playing a character that is immature, rebellious, and difficult to manage. This could be a function in a motion picture, a play, or even in his individual life. It is most likely that he is feeling overwhelmed by the expectations of this role and is all set to move on to something else. He is likely feeling frustrated and tired from needing to continuously act out this character and is all set to take on a new obstacle. This quote is a reminder that often it is needed to take a break from a role that is no longer serving us and to move on to something new.