What does harris's attempt to sing comic song tell us about his character?

Harris singing of songs illustrates his self-confidence. He can't sing, but he believes that everyone should hear him just once.... then die.

“Not a bit of it.  Serve ’em all jolly well right, and I’d go and sing comic songs on the ruins.”

I was vexed to hear Harris go on in this blood-thirsty strain.  We never ought to allow our instincts of justice to degenerate into mere vindictiveness.  It was a long while before I could get Harris to take a more Christian view of the subject, but I succeeded at last, and he promised me that he would spare the friends and relations at all events, and would not sing comic songs on the ruins.

You have never heard Harris sing a comic song, or you would understand the service I had rendered to mankind.  It is one of Harris’s fixed ideas that he can sing a comic song; the fixed idea, on the contrary, among those of Harris’s friends who have heard him try, is that he can’t and never will be able to, and that he ought not to be allowed to try.

When Harris is at a party, and is asked to sing, he replies: “Well, I can only sing a comic song, you know;” and he says it in a tone that implies that his singing of that, however, is a thing that you ought to hear once, and then die.