When Janice asks the guys who "almost had sex" with each other, we see a flashback of what happened a year previous the premiere of the series.
Friends Episode 6 "The One with the Flashback" tells the story of how Joey ended up being Chandler's roommate (thanks to Mr. Heckles), how did Ross discovered Carol is a lesbian, how Monica met with Rachel before they met in the show's premiere after years after high school. It also tells how Ross almost slept with Phoebe, how Monica almost slept with Joey, and how Chandler almost slept with Rachel. This episode is an amazing episode. With everything oging on, and was so funny! Season 3 is great!