After Mr Weasley and Mr Malfoy have their fistfight in Flourish and Blotts, Hagrid says:
"Yeh should've ignored him, Arthur...Rotten ter the core, the whole family, everyone knows that. No Malfoy's worth listenin' ter. Bad blood, that's what it is. Come on now - let's get outta here."
(Chamber of Secrets, Chapter 4, At Flourish and Blotts).
Now I've always understood Hagrid to be saying, in effect, "Don't concern yourself with the Malfoys. They're just a bunch of troublemakers." 'Bad blood' here would refer to the Malfoys' natural proclivity for starting arguments with their taunts and insults. Or he could mean that there is bad blood (i.e. ill-feeling, enmity and hostility) between the Malfoys and the Weasleys - and that that's the way it's always going to be.
Then it struck me that he could mean something else. He could be saying that the Malfoys are inherently spiteful, argumentative or disdainful simply because they are pure-bloods. In other words, he thinks that the 'blood' of the Malfoys makes them what they are.
Ordinarily, I would dismiss this interpretation as over-thinking Rowling/Hagrid's choice of words, since prejudice of this sort is out of character for Hagrid. However, it's difficult to gloss over Hagrid's statement when you consider the following fact:
Discrimination based on blood purity is the main central theme of Harry Potter and the Chamber of Secrets.
It seems impossible that Rowling or her publisher could have simply slipped this sort of phrase in without thinking about it, considering the subject matter of the book. Purebloods like the Malfoys discriminate against half-bloods and Muggle-borns. The 'good guys' like Dumbledore don't differentiate between people based on their ancestry. So, as I say, Hagrid's language here doesn't fit. Yet are we really to suppose that it was entirely coincidental?
So is there any way of supposing what Hagrid actually meant when he said "bad blood"? Has Rowling commented on this at all?
Note: I'm not suggesting that Hagrid was prejudiced against purebloods in general. I'm just asking whether he was in this instance.