Thomas was doing his level best to not get irritated and not yell at Cimorene and not be a poor guest, but if she insisted on needling him, he wasn't sure his level best would be near enough.
"I'm going to be true to my nature. All I want is to see a dragon which will likely be very interesting, and then go home. I'm sure I can restrain any impulses that might lie in my princeliness to slay one, but I sure as hell won't be doing it to prove anything to you. I don't need to. Being a prince doesn't define me."