"But you make a mistake if you do not see that it was written seriously." His father glanced across at him, where he sat with his heavy, plain face, his long arms and short legs, and the sight merely irritated him.

With his passion for convention (and one of the most important conventions was that Combers should be fine, strapping, normal people) he hated the thought that it was his son who presented that appearance.
And his son's mind seemed to him at this moment as ungainly as his person.

Again, very unwisely, he laughed, still thinking to carry this off by the high hand.
"Yes, but I can't take that rubbish seriously," he said.

"I am asking your permission now to inquire, without any nonsense, into what you mean." Michael frowned.

He felt the insincerity of his father's laugh, and rebelled against the unfairness of it.