[Mettaton is no closer to calming down from one second to the other, but when Frisk calls him weird, something else in him seems to snap, and he gives them such a nasty look that it could probably burn through them with the sheer negativity the expression exudes.]

...You know, that is not a very polite thing to tell someone. Is that all you think of me? Weird?

[Despite the ugly look on his face, Mettaton speaks calmly. His fingers even steeple, held up around his face in a pensive expression. He seems to be attempting to calm himself.

It's no less threatening.]

Little human, I think it prudent that you leave, or apologize. Both would be preferred...but this charade has gone on long enough. I will tolerate it no longer.