4x13 "The One with Rachel's Crush"

As the guys and the girls switched apartments, Monica told the guys they have to be the hosts only for her to want to become the hostess again. Chandler breaks up with Kathy after seeing her having simulated sex on stage with another man. Kathy tells Chandler that it is just her job, and tells Chandler to call her when he can grow up. It is later revealed that Kathy wasn't sleeping with him, but starts to after her and Chandler's dispute, causing Chandler to say, that their "second fight ... is going to be A BIG ONE!" Rachel has a crush on Joshua, a handsome customer and even ponders asking him out.