At the beginning of the episode Chandler was coming Monica’s flat and saw Rachel naked. She was embarrassed. In the café, Chandler also spoke about this accident. Phoebe got acquainted with a psychiatrist. The friends hated Phoebe's new boyfriend because of his annoying analysis of their lives. Eventually, she also realized he was actually an unpleasant person who enjoyed psychological power over people, and Phoebe broke up with him.
After Joey's father came to visit, Joey discovered that his father was cheating on his mother. Joey interrupted a telephone conversation he believed his dad was talking with his mother, and found out about his father's mistress, Ronni. Ronni met Joey on her way to meet his dad, and Joey did all he could to prevent them from relationship. Joey's mother then showed up to confess how she knew everything. She also admitted to Joey that she was okay with this situation.
As we know, Chandler saw Rachel naked. Rachel opened the door while Chandler was in the bathroom to get revenge on him. But this was Joe. Then Joe came to get revenge on Rachel, but this time he saw Monica. Then Monica saw Joe's father.