6x22 "The One Where Paul's the Man"

Paul tells Ross that he disapproves of Ross' relationship with Elizabeth and threatens to have him fired if they continue seeing each other. Deciding to continue their relationship, Ross and Elizabeth sneak away to her family's cabin, not knowing Paul and Rachel have the same idea. The girls put their names down on a wedding list that gets back to Chandler, who promptly bolts. Eventually Monica finds him and calms him down, little realizing that Chandler is actually planning to propose.