They are very rude, speaking as though he is not there. But it does not bother him; it is not as though the police do not have worse said about them, and to their faces.

And he returns the look of disgust in kind. He has no objections to Prouvaire's race, more that he is a stupid young thing that dresses outlandishly. Also, he does not seem to be adept at picking locks.

'Where did you learn this?' he asks, in what is almost a conversational tone. 'And for what purpose?'

Why would anyone honest need to know it? And to Enjolras, he adds, 'it is not I that needs pity. Nor lessons in manners.'

This last is true. Javert is perfectly aware of what constitutes good manners, he simply chooses who is worth exercising them on.