[Aziraphale glances up, and gains a mildly scolding look, reading through the tone to the words immediately.] Now, there's no call to be insulting, dear boy. Dust can be rather damaging to paper.

And actually, this is not the ordinary library, just my private collection. You're welcome to peruse it if you can respect the books. [He doesn't seem to be holding the slight against him, despite what he's saying; Aziraphale has brightened up by the end of his sentence, apparently eager to share his texts with others.]