Do they give sass lessons in Azkaban or something?
People always forget that Sirius Black is the king of sass and drama.
But think about this.
Chemistry isn’t a Hogwarts subject. Potions is. But of course Sirius knows that Snape is a half-blood, and that he hates being a half-blood. Not only is Sirius being a sassy motherfucker but he says precisely the thing he knows will push Snape’s buttons the most - he mentions something Muggle related.