S4E14 : Eric's Hot Cousin

Eric' cousin Penny, whom he used to tease unmercifully when they were younger, comes for a visit, and she's...grown some. All the guys are infatuated with her, much to Donna and Jackie's dismay. Jackie and Donna try to be hotter than Penny, with disasterous results. Kitty, feeling like she's not needed, wants to get a pet.