] I'm inclined to believe the latter--JT is just that egotistical, that self-absorbed, that clueless ... The thought that he might be turned down never seems to register.

Yes, John Thorpe is an idiot, I think we all agree on that! ;-) But I do think he was a bit nervous as well. JA says

"Catherine wished him a good journey. Without appearing to hear her, he walked to the window, fidgeted about, hummed a tune, and seemed wholly self-occupied."

These seems the actions of a nervous man, or at the least, an uncomfortable one. But however he began (and bumbled through) he ended feeling confident.

"...she hurried away, leaving him to the undivided consciousness of his own happy address, and her explicit encouragement."

] More so since John's hearing no more or less than what he wants to. ;-)