In the scene where Jeff finally converses with Chrissy, the train is clearly sitting still the whole time (you can see the same people standing at the station in the background). Steven Moffat explained that the train made too much noise when it moved, making the dialogue inaudible, so they had to film the whole scene with the train standing still.
Steve: Here on Earth, there's a gap between seeing someone you like and having sex with them that we like to call conversation... In Jeff's case, it can last up to 10 years.
Jane: I've always wanted to date a gynaecologist. I wanna know I'm special.
Jeff: I have the key to the Gates Of Paradise! But I've got too many legs!
Sally: I can't stay friends with men who know what I'm like in bed. I'd have to kill them.
Jeff: This is the curse of Jeff Murdock. I meet the woman of my dreams and I can't take my trousers off.
Patrick: You've seen this woman on the train and you find her attractive, yeah?
Patrick: And you haven't had sex with her?
Patrick: You see my problem?
Steve: Jeff, Jeff, I know about the giggle loop, the sock gap, the nudity buffer, and what you said to Audrey Watkins. Believe me, there is nothing you can possibly say that will surprise me. What's gone wrong this time?
Jeff: I've got too many legs.
Steve: Jeff, I know about the Giggle-Loop, the Sock-Gap, the Nudity-Buffer and what you said to Audrey Watkins, believe me, there is nothing you can possibly say that would surprise me.
Steve is referring to some of Jeff's creations from season 1:
Giggle-Loop - Episode 3
Sock-Gap - Episode 2
Nudity-Buffer - Episode 5
as well as the "worst jab-line in the history of sex" previously mentioned in episode 5 of the 1st season:
Jeff to Audrey Watkins at Steve's flat-warming some time ago: "You are so gorgeous, you should be embalmed".
Was intented to be remade as the 11th episode of AmeriCoupling, but the show was canceled soon before this episode was to tape.