Which episode?

Which episode includes this exchange? The DVD synopses were unhelpful.

Steve: You bring these things [throw pillows] into our homes. They sit on our chairs. They watch our televisions. Now, I just need to know, on behalf of all men everywhere, I just need to ask, please... What are they for? I mean, look at them! Look at the chubby little bastards! Just sitting around everywhere! What are they, pets for chairs?

[to shop assistants]

Steve: Come on, you sell them. What are they for?

Junior Shop Assistant: Well...

Senior Shop Assistant: You sit on them.

Steve: Ah! Ha ha ha! You see, that's where you're wrong! Nobody sits on them. Okay, watch this. Here's the cushion. I'm putting it on the sofa. Now watch me. I'm sitting down. And what do I do on my final approach? I - oh! - move the cushion! You see? It's not involved! It's not part of the whole sitting process. It just lies there. It's fat litter! It's a sofa parasite!

Jane: It's, you know... padding.

Steve: Oh, padding! Now, that's interesting, Jane. See, I like padding. If I was, say, an American Football player, and all those big bastards running at me, I would say "give me some of that padding and be quick about it." If my job involved bouncing down jagged rocks I would say "in view of those jagged rocks down there, I'll have some of that padding, thank you very much." But Susan, Sally, Jane, this is a sofa. It is designed by clever scientists in such a way as to shield the unprotected user from the risk of skin abrasions, serious head trauma, and, of course...

[drops behind sofa, then sticks head out]

Steve: Daleks. Trust me girls, trust me on this one: you do not need padding to tackle upholstery. So please - once and for all, tell me why on Earth you would want me to sit on one of these?

Susan: Because, if you pressed it firmly against your bottom, it might stop you talking!

_______
The sun is shining... but the ice is slippery.