4x18 "The One with Rachel's New Dress"

Joshua invites Rachel to his parents' house, who are said to be out of town. She changes into a more revealing dress and Joshua and his parents walk in, much to her embarrassment. Phoebe is offered the chance to name one of the triplets and chooses 'Chandler' over 'Joey' when Chandler realizes he has a horrible name and wants to change it, much to Phoebe's disapproval. When Phoebe leaves, it is revealed that it was just a plan by Chandler to get her to choose his name. Ross suspects Emily of having an affair with Carol's wife Susan.