The intent is to focus up and defend his relative state of sobriety. But, the part of his brain capable of that is apparently sitting way in the back while the stupid side takes the wheel.

Between Vincent calling him out and the incredible mental image of baby Seth that has been gifted to him, the chuckling just gets worse. Which doesn't exactly feel great on his torn up organs, but he can't bring himself to care much about that fact beyond distantly noting it.

"...Got called a wastrel..."

By normal-people standards, it's a good round of quiet chuckling. By Irahl standards, it's a giggle-fit.