As Charlie gains intelligence, it suddenly dawns on him at the work party that his friends Frank and Joe invite him out to events so that they can make fun of him and laugh at him, not because they really consider him a friend.
He tries to avoid drinking, because he remembers the bad experience he had the last time he went to a party with them and drank. However, they have clearly put something into his Coke, because it tastes strange to him.
Frank and Joe encourage him to dance with a woman named Ellen, and Charlie does, but people keep trying to trip him. As Charlie looks up at Joe's laughing face, he realizes he is being laughed at, not with. Charlie blushes. Nobody has seen him embarrassed before:
Everyone was looking at me and laughing and I felt naked. I wanted to hide myself. I ran out into the street and I threw up. Then I walked home. It's a funny thing I never knew that Joe and Frank and the others liked to have me around all the time to make fun of me. Now I know what it means when they say "to pull a Charlie Gordon."
When he gets home, Charlie writes in his journal that he feels ashamed.