There are moments in A Connecticut Yankee in King Arthur's Court in which Hank reveals to us that he is, pretty much, a confidence man. In this way, he is a bit like all of us. I mean, we all - at one point or another - try to make ourselves look good to others, or at least try to humiliate our "rivals."
So far, Hank has made himself a conman by humiliating Merlin. His very first con is when he destroys Merlin's tower. He describes to us what he did to set up the tower to be destroyed, obviously keeping it secret from everyone else. We are fully aware of what is going on and that the destruction of the tower was nothing more than chemistry at work. However, Hank is in the sixth century. Chemistry in the sixth century was witchcraft. Because of this, the townspeople believed that Hank had incredible powers and that he used them to destroy the tower.
What makes this a con is that Hank did this fireworks show with Merlin - who is pretty much his rival in the story - standing right next to him. Of course, it wasn't bad enough that Hank destroyed Merlin's tower, but he had Merlin try and "save" his tower with his magic and then blew it up anyways. Hank humiliated Merlin in front of everyone, making himself look all powerful while leaving the impression that Merlin was useless.
As things would have it, Hank's cons would not end there. Once again he humiliated Merlin when he "fixed" the dried-up well. After going down into the well, Hank described the problem to the reader and how simple it was to fix (simple crack in the wall was letting all of the water out). However, instead of leaving it at that and simply fixing the well, he had to come along and put on another "magic" show. Just like the show with Merlin's tower, Hank had Merlin have a try at fixing the well himself. Merlin, being the trusted wizard that we is in the eyes of the people, tried all sorts of "spells," but eventually gave up claiming that a powerful demon had cursed it. After some time preparing, Hank began his magic show, setting off the fireworks and casting his "spells" which were more like horribly butchered German. Once again, Hank prevailed as the dominant wizard, at least in the eyes of the locals.
It is apparent that Hank is a confidence man. I mean, let's face it, he does show off quite a bit and makes Merlin look pathetic. With that in mind, he is a bit like the rest of us. Honestly, who doesn't want to show off? Deep down, we all want to make ourselves look good. We've all had those moments at one point when we do something amazing that has people go "WOW" or make those we don't get along with too well feel somewhat pathetic.