2x22 "The One with the Two Parties"

Rachel's birthday is coming up, and Monica is planning a classy party for her and it is decided not to invite her father as her mother Sandra is already coming and the two are at a point in their divorce when they can't stand to be in the same room as each other. However, when Rachel's dad turns up unexpectedly, another impromptu party is set up at Chandler and Joey's for Dr. Green to attend to keep him away from his estranged wife. Things quickly start to go wrong when Sandra worries after seeing Ross fetching things for Dr. Green and believes her daughter is dating a man who reminds her of her father, while the guests at Monica's party quickly tire of the host sucking the fun out of the event with her dull games and strict rules and begin fleeing to Joey and Chandler's more laidback party instead. In the end, despite a few close calls, the six successfully manage to get the couple out of both parties without bumping into each other.