Boccaccio offers an "Author's Epilogue" after the conclusion of the storytelling game and the return of the brigata to Florence. It's part of the narrative frame or cornice that began with the Prologue, and it has the same intimate, chatty tone. But there's one major difference: Boccaccio is even more roguish and devil-may-care in his address to his critics. He's also a lot more vulgar, as though the stories he's penned over the course of the work have "liberated" his thinking.
Boccaccio addresses his critics twice before: in the Prologue (where he explains, rather than defends, his choices) and in the Introduction to Day Four (where he defends his attention to ladies). Now, at the conclusion of the work, he defends his more vulgar stories and language by reassuring us that things are only evil when they're used with evil intent. He also removes the blame for such ribald (we love that word) stories from himself by saying that he's only recording the stories as they were told by the brigata.
Of course he's speaking tongue-in-cheek, but it's also a nod to the idea that writers at the time didn't typically innovate—they merely transmitted or adapted things from their sources. Such a reliance on "authority" is considered the gold standard of responsible writing in the Middle Ages, and Boccaccio has no problem using that to his advantage. In fact, he uses a traditional rhetorical structure to create his Prologue and Epilogue and then invests it with attitude to get his point across. And what's that point exactly? It's up for interpretation, of course, but we like this one: "I don't care what you think."