I notice a lot of these "which episode was this in?" posts, most likely do to the humor having almost nothing to do with the plot, hehe...
But, I have one to add... Peter and Brian are standing in the doorway and Peter says something about how he read it in a book somewhere (don't remember what "it" was), and Brian looks at him and says something along the lines of, "don't you mean that you read it... NO where?!" and peter is like "oh, yeah"
So.... name that episode! Danke schon.