Answer:
Because he is not wearing shoes.
Step-by-step explanation:
In American Born Chinese, the Monkey King is an important character. However, he is faced with a conflict. Even though he is a king (and a god), he is not allowed to go to a party hosted by other gods because he is not wearing any shoes, and because he is a monkey. This upsets him, as the Monkey King is extremely conceited and believes himself to be entitled to divine rights.