7x11 "The One with All the Cheesecakes"

Rachel and Chandler get hooked on cheesecakes meant for someone else. David (Hank Azaria), Phoebe's Scientist Guy, comes into town for just one night and wants to have dinner with Phoebe when she already has plans with Joey. Monica's cousin Frannie, with whom she was once best friends, is getting married, and she is not invited. As it turns out, her husband is Stuart, an old flame who slept with Monica once.