In the one with the flashback, season 3, Janice asks everyone if they've ever done it with anyone from the group. They all say they haven't and Rachel makes a comment about Ross not putting out. However, in the second season in the one where Ross and Rachel...you know, he apparently does put out, it's even in the title.
Of course Ross & Rachel have done it. This is NOT a slip up they are a couple so Janice didn't mean them. She meant the rest of the non attatched group.
Yeah..this is NOT a slip up..When Rachel said "Yeah and if that doesn't change soon, I'm gonna dump you for someone who puts out" she was being sarcastic...this is not a slip up.