Trip to Chicago

In a mental institution a nurse walks into a room and sees a patient acting like he's driving a car. The nurse asks him, "Charlie, what are you doing?" Charlie replied, "Driving to Chicago!" The nurse wishes him a good trip and leaves the room. The next day the nurse enters Charlie's room just as he stops driving his imaginary car and asks, "Well Charlie, how are you doing?" Charlie says, "I just got into Chicago". "Great," replied the nurse. The nurse leaves Charlie's room and goes across the hall into Bob's room, and finds Bob sitting on his bed furiously masturbating. Shocked, she asks, "Bob, what are you doing?!" Bob exclaims, "I'm screwing Charlie's wife while he's in Chicago!"