A "deb's delight" was something Ben Jackson claimed he wasn't when Polly Wright — whom he had only just met — invited him to lunch at the Post Office Tower in July 1966. Polly responded by regarding him in his HMS Teazer cap and uniform, happily smiling, and saying, "I can see that." (TV: The War Machines)
Behind the scenes[]
In context, the remark reinforced one of the central aspects of their relationship: her upper class upbringing — which he usually highlighted by calling her "Duchess" — and his working class life as a sailor. Though undefined in episode 2 of The War Machines, its usage squares with the standard definition of a single, successful, well-bred man that would be attractive to a debutante.