Season 8: Episode 173: The One With The Videotape
Ross's and Rachel's attempt to explain to the gang how they wound up in bed together six weeks earlier quickly devolves into an argument over who came on to whom -- until Ross shocks the room by announcing that he has the whole encounter on videotape. Meanwhile, Monica and Chandler return from their honeymoon, excited at the prospect of hanging out with another just-married couple they met on the flight home...until they discover that their newfound "friends" gave them a fake phone number.