I did laugh at that line. It is very clever the way Austen introduces Robert Ferrars to Elinor and the first-time reader before knowing who he really is. We get to form our impressions of him without knowing his connections and it is not a favorable one. Robert Ferrars is obviously a fastidious man and I can see him in front of a mirror carefully picking his teeth even when there is nothing to be picked (shades of Sir Elliot). And not just any case will do. The whole toothpick case scene smacks of foppery. "...and on the puppyism of his manner in deciding on all the different horrors of the different tooth-pick cases presented for his inspection..." :-)