Biff's diary entry after this pivotal moment would probably indicate just how heartbroken he was by this discovery. In particular, it should address the fact that he now views his father as a phony, and has lost a great deal of respect for him. After all, when he discovers his father with the woman, he storms out of the room shouting, "You fake! You phony little fake! You fake!” While their relationship is extremely complex, this is obviously an important moment in its development, and the diary entry should reflect this. Before it occurs, we see that Biff in many ways has respect for his father. He had come to him, after all, asking him to persuade his math teacher to pass him, because he admired his father's way with words. In summation, this is an extremely traumatic event in Biff's life, and the disappointment and anger he feels should not be understated.