"My Last Duchess" reminds us of an arrogant speech by a witty guy who knows he’s witty. Because it’s written in iambic pentameter, and because it has so many dramatic qualities, it reminds us of a Shakespeare play. We imagine the most pompous actor we’ve ever seen standing in the middle of a stage, planting his feet wide apart, and declaiming his lines with a lot of pretentious self-importance. There’s no doubt that the Duke is self-important. After all, what makes him angry about the last Duchess's behavior is that she thinks anyone could be important as important as he is. Toward the end of the poem, as the Duke walks his listener downstairs toward the rest of the party, he points out one last piece of art in his collection:
Notice Neptune, though,
Taming a sea-horse, thought a rarity,
Which Claus of Innsbruck cast in bronze for me! (54-56)
We can just see the Duke pointing proudly at the statue, speaking each of his phrases with distinction, and crackling those hard consonants ("Which Claus of Innsbruck cast in bronze for me!") for all he’s worth.