Season 2: Episode 46: The One With The Two Parties
It's Rachel's birthday and Monica wants to throw her a party. Trouble is, Rachel's parents are divorcing and cannot remain civil to one another, so Monica plans to only invite Rachel's mom. Rachel's dad shows up unexpectedly, and the gang sets up an impromptu "second party" at Joey and Chandler's place for him to go to. Ross suffers through several awkward situations with Rachel's dad while trying to keep him from discovering the other party. Rachel ends up bouncing back and forth between the two parties and winds up depressed when she realizes this is how the rest of her life will be. Meanwhile, Phoebe starts sneaking people out of Monica's boring party (a la a concentration camp) and over to the wild and fun party at the guys' place.