It seems ‘blockhead’ was a popular insult in the nineteenth century. In our corpus Emma tops the league table of blockheads with three, but Austen also employs it in Mansfield Park and Sense and Sensibility, where the caddish Willoughby proclaims:

though I have been always a blockhead, I have not been always a rascal

So blockheads may not be rascals, but it seems they are often consummate and conceited types. Paul Dangerfield taunts Lowe in The House by the Churchyard:

I’ve evidence which escaped you, conceited blockhead

You arrest me upon the monstrous assertion of a crazy clerk, you consummate blockhead!

Similarly, in Bleak House, Dickens has Mr. Boythorn let rip about his blockhead neighbour, Sir Leicester Dedlock:

that fellow is, and his father was, and his grandfather was, the most stiff-necked, arrogant imbecile, pig-headed numskull, ever, by some inexplicable mistake of Nature, born in any station of life but a walking-stick’s!

If that wasn’t enough, he continues:

The whole of that family are the most solemnly conceited and consummate blockheads! But it’s no matter; he should not shut up my path if he were fifty baronets melted into one and living in a hundred Chesney Wolds, one within another, like the ivory balls in a Chinese carving.

Brönte gives us another apologetic blockhead in the form of Mr. Rochester, who blames his block-headedness for his marriage to Bertha:

I had marked neither modesty, nor benevolence, nor candour, nor refinement in her mind or manners–and, I married her:–gross, grovelling, mole-eyed blockhead that I was!

Edgeworth is also fond of blockheads, but she deserves recognition for using the collective form in Ennui:

What a parcel of blockheads you all are!

For even more blockheads, The Guildhall Library’s blog gives a run down of The Book of Blockheads (1863) by satirist and Punch illustrator Charles Bennett. See here for a preview on Google Books.