one of those French phrases I've never totally grasped, here used nounily (sure, adjectives and nouns - inseparable)

"I shook [her] hand. "How do you do," I said with as much conventionality as I could muster, as if an ostentatious show of comme il faut might minimize her son's aberrancy and the dark, inordinately troubling gap in my smile and the collapse of law and order betokened by the detectives surrounding us and, this particular slope being a slippery one, the hellishness of the world." O'Neill, ibid

here, correctness in deportment or behavior?