The One With The Invitation - 7.3
According to IMDb, the absolutely worst episode of Friends is "The One with the Invitation." Again, it's another episode that simply forces the characters to reminisce on pre-filmed episodes. Rachel and Ross examine their past relationship as Ross after Emily send out their wedding invitations.
Emily is surprised that Ross still wants to invite Rachel given their past, while Rachel simultaneously debates on whether or not to fly to London for their wedding. Ultimately, Rachel decides not to once she realizes she still has feelings for Ross and can't witness him getting married to someone else.