Rei calls out Usagi for reading a book, telling Usagi that hell must have frozen over for her to read anything other than manga. Usagi responds with the above quote and embarrasses Rei.

I don't often buy Rei stuff but this came in a lot with other Rei cels. It's sorta amusing to me that in an episode primarily featuring Makoto that the only artwork I own is of Rei ^^'

From Episode 134 - "Makoto no Yujou! Tenba ni Akogareta Shoujo"(Makoto's Friendship! The Girl who Admired Pegasus).