The professional conversationalist — "that your blithe inattention to your…"
‘… that your blithe inattention to your own dear grammatical mother’s cavortings with not one not two but over thirty Near Eastern medical attachés…?’
Context
Mid-rant, JOI's epithet for Avril is "your own dear grammatical mother" — grammar as her identifying attribute even inside her husband's paranoid accusations of infidelity. (The leading ellipsis is the text's own, JOI resuming mid-sentence.) One word doing the work of the whole Militant-Grammarians dossier to come.