I think that you can find specific elements of the narration that helps to show Curley as someone who is fundamentally frail from the emotional point of view. In chapter 2, Curley sees the size of Lennie and wishes to pick a fight immediately, threatened by his size. The fact that he would be so openly hostile to Lennie, who has not done or said anything, is a reflection of his "poser" state. Curley simply cannot deal with the fact that Lennie is so much bigger than he is. When he actually does confront Lennie, it becomes evident that Curley not only has anger problems, but also that he is weaker than Lennie. Curley is so angry, filled with irrationality, that when he sees Lennie smiling, he automatically thinks that Lennie is laughing at him. His fighting Lennie is yet another example of how emotionally weak he really is. This weakness is manifested in a physical form when George tells Lennie to fight back. Steinbeck's description of this confrontation reveals how weak Curley actually is:
... [Curley was] flopping like a fish on a line, and his closed fist was lost in Lennie’s big hand.
In this, the ultimate statement about Curley's moral and physical weakness is evident, proving him to be no more solid than the "glove full of Vaseline" that is always a part of him in the eyes of the other men.