Season 9: Episode 214: The One with the Donor
Joey arranges for a reluctant Rachel to help Charlie shop for some new clothes. Phoebe comes along as well, and Charlie overhears Phoebe and Rachel talk about Rachel's feelings for Joey; but Charlie thinks it was Phoebe who has feelings for him. Phoebe is invited to a party which Mike will also be attending, and stresses about looking great but pretending to be over him. But on her way, she runs into her old flame, David (the Scientist guy), and changes her plans. Ross has a chance to be the keynote speaker at a Paleontology convention in Barbados; when he's making his pitch to the deciding professor, it puts him to sleep. Chandler and Monica visit their Doctor about reproductive options, and begin searching for a sperm donor. Chandler invites a likely but unsuspecting candidate (Zack) to dinner, and he gets a little creeped out by the odd questions Chandler and Monica are asking. In the end they decide to adopt.